What has happened to the Klopp press?

Originally published on StatsBomb.

When asked how his Liverpool team would play by the media horde who greeted his unveiling as manager two years ago, Jürgen Klopp responded:

We will conquer the ball, yeah, each fucking time! We will chase the ball, we will run more, fight more.

The above is a neat synopsis of Klopp’s preferred style of play, which focuses on pressing the opponent after losing the ball and quickly transitioning into attack. It is a tactic that he successfully deployed at Borussia Dortmund and one that he has employed regularly at Liverpool.

However, a noticeable aspect of the new season has been Liverpool seemingly employing a less feverish press. The Anfield Index Under Pressure Podcast led the way with their analysis, which was followed by The Times’ Jonathan Northcroft writing about it here and Sam McGuire for Football Whispers.

Liverpool’s pass disruption map for the past three seasons is shown below. Red signifies more disruption (greater pressure), while blue indicates less disruption (less pressure). In the 2015/16 and 2016/17 seasons, the team pressed effectively high up the pitch but that has slid so far this season to a significant extent. There is some disruption in the midfield zone but at a lower level than previously.

LFC_dxP.png

Liverpool’s zonal pass completion disruption across the past three seasons. Teams are attacking from left-to-right, so defensive zones are to the left of each plot. Data via Opta.

The above numbers are corroborated by the length of Liverpool’s opponent possessions increasing by approximately 10% this season compared to the rest of Klopp’s reign. Their opponents so far this season have an average possession length of 6.5 seconds, which is lower than the league average but contrasts strongly with the previous figures that have been among the shortest in the league.

Examining their pass disruption figures game-by-game reveals further the reduced pressure that Liverpool are putting on their opponents. During 2015/16 and 2016/17, their average disruption value was around -2.5%, which they’ve only surpassed once in Premier League matches this season, with the average standing at -0.66%.

LFC-xP-17-18

Liverpool’s game-by-game pass completion disruption for 2017/18 English Premier League season. Figures are calculated for zones above Opta x-coordinates greater than 40. Data via Opta.

The Leicester match is the major outlier and examining their passing further indicates that the high pass disruption was a consequence of them attempting a lot of failed long passes. This is a common response to Liverpool’s press as teams go long to bypass the pressure.

Liverpool’s diminished press is likely a deliberate tactic that is driven by the added Champions League matches the team has faced so far this season. The slightly worrisome aspect of this tactical shift is that Liverpool’s defensive numbers have taken a hit.

In open-play, Liverpool’s expected goals against figure is 0.81 per game, which is up from 0.62 last season. Furthermore, their expected goals per shot has risen to 0.13 from 0.11 in open-play. To add further defensive misery, Liverpool’s set-piece woes (specifically corners) have actually got worse this season. The team currently sit eleventh in expected goals conceded this season, which is a fall from fifth last year.

This decline in underlying defensive performance has at least been offset by a rise on the attacking side of 0.4 expected goals per game to 1.78 this season. Overall, their expected goal difference of 0.79 this season almost exactly matches the 0.81 of last season.

Liverpool’s major problem last season was their soft under-belly but they were often able to count on their pressing game denying their opponents opportunities to exploit it. What seems to be happening this season is that the deficiencies at the back are being exploited more with the reduced pressure ahead of them.

With the season still being relatively fresh, the alarm bells shouldn’t be ringing too loudly but there is at least cause for concern in the numbers. As ever, the delicate balancing act between maximising the sides attacking output while protecting the defense is the key.

Klopp will be searching for home-grown solutions in the near-term and a return to the familiar pressing game may be one avenue. Given the competition at the top of the table, he’ll need to find a solution sooner rather than later, lest they be left behind.

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Under pressure

Originally published on StatsBomb.

Models that attempt to measure passing ability have been around for several years, with Devin Pleuler’s 2012 study being the first that I recall seeing publicly. More models have sprung up in the past year, including efforts by Paul Riley, Neil Charles and StatsBomb Services. These models aim to calculate the probability of a pass being completed using various inputs about the start and end location of the pass, the length of the pass, the angle of it, as well as whether it is played with the head or foot.

Most applications have analysed the outputs from such models from a player passing skill perspective but they can also be applied at the team level to glean insights. Passing is the primary means of constructing attacks, so perhaps examining how a defense disrupts passing could prove enlightening?

In the figure below, I’ve used a pass probability model (see end of post for details and code) to estimate the difficulty in completing a pass and then compared this to the actual passing outcomes at a team-level. This provides a global measure of how much a team disrupts their opponents passing. We see the Premier League’s main pressing teams with the greatest disruption, through to the barely corporeal form represented by Sunderland.

Team_PCDgraph

Pass completion disruption for the 2016/17 English Premier League season. Disruption is defined as actual pass completion percentage minus expected pass completion percentage. Negative values means opponent’s complete fewer passes than expected. Data via Opta.

The next step is to break this down by pitch location, which is shown in the figure below where the pitch has been broken into five bands with pass completion disruption calculated for each. The teams are ordered from most-to-least disruptive.

PressureMap

Zonal pass completion disruption for 2016/17 English Premier League season. Teams are attacking from left-to-right, so defensive zones are to the left of each plot. Data via Opta.

We see Manchester City and Spurs disrupt their opponents passing across the entire pitch, with Spurs’ disruption skewed somewhat higher. Liverpool dominate in the midfield zones but offer little disruption in their deepest-defensive zone, suggesting that once a team breaks through the press, they have time and/or space close to goal; a familiar refrain when discussing Liverpool’s defense.

Chelsea offer an interesting contrast with the high-pressing teams, with their disruption gradually increasing as their opponents inch closer to their goal. What stands out is their defensive zone sees the greatest disruption (-2.8%), which illustrates that they are highly disruptive where it most counts.

The antithesis of Chelsea is Bournemouth who put together an average amount of disruption higher up the pitch but are extremely accommodating in their defensive zones (+4.5% in their deepest-defensive zone). Sunderland place their opponents under limited pressure in all zones aside from their deepest-defensive zone where they are fairly average in terms of disruption.

The above offers a glimpse of the defensive processes and outcomes at the team level, which can be used to improve performance or identify weaknesses to exploit. Folding such approaches into pre-game routines could quickly and easily supplement video scouting.

Appendix: Pass probability model

For this post, I built two different passing models; the first used Logistic Regression and the second used Random Forests. The code for each model is available here and here.

Below is a comparison between the two, which compares expected success rates with actual success rates on out-of-sample test data.

Actual_vs_Expected

Actual versus expected pass success for two different models. Data via Opta.

The Random Forest method performs better than the Logistic Regression model, particularly for low probability passes. This result is confirmed when examining the Receiver Operating Characteristics (ROC) curves in the figure below. The Area Under the Curve (AUC) for the Random Forest model is 87%, while the Logistic Regression AUC is 81%.

xPass_AUC

Receiver Operating Characteristics (ROC) curves for the two different passing models. Data via Opta.

Given the better performance of the Random Forest model, I used this in the analysis in the main article.

Networking for success

In my previous post, I described my possession danger rating model, which classifies attacks according to their proximity to goal and their relative occurrence compared to other areas of the pitch. Each possession sequence in open-play is assigned a value depending on where it ends. The figure below outlines the model, with possession sequences ending closer to goal given more credit than those that break down further away.

Map of the pass weighting model based on data from the English Premier League. Data via Opta.

Map of the pass weighting model based on data from the English Premier League. Data via Opta.

Instead of just looking at this metric at the team level, there are numerous ways of breaking it down to the player level.

For each possession, a player could be involved in numerous ways e.g. winning the ball back via a tackle, a successful pass or cross, a dribble past an opponent or a shot at goal. Players that are involved in more dangerous possessions may be more valuable, particularly when we compare them to their peers. When viewing teams, we may identify weak links who reduce the effectiveness of an attack. Conversely, we can pick out the stars in a team or indeed the league.

Networking

One popular method of analysing the influence of players on a team is network analysis. This is something I’ve used in the past to examine how a team plays and who the crucial members of a team are. It looks at who a player passes the ball to and who they receive passes from, with players with many links to their teammates usually rated more highly. For example, a midfield playmaker who provides the link between a defence and attack will often score more highly than a centre back who mainly receives passes from their goalkeeper and then plays a simple pass to their central defensive partner.

In order to assess the influence of players on attacking possessions, I’ve combined the possession danger rating model with network analysis. This adjusts the network analysis to give more credit to players involved in more dangerous attacks, while also allowing us to identify the most influential members of a team.

Below is an example network for Liverpool last season during a 10 match period where they mainly played in a 3-4-3 formation. The most used eleven players during this period are shown according to their average position, with links between each player coloured according to how dangerous the possessions these links contributed to were.

Possession network for Liverpool for the ten matches from Swansea City (home) to Burnley (home) during the 2014/15 season. Lines are coloured according to the relative danger rating per each possession between each player. Player markers are sized by their adjusted closeness centrality score.

Possession network for Liverpool for the ten matches from Swansea City (home) to Burnley (home) during the 2014/15 season. Lines are coloured according to the relative danger rating per each possession between each player. Player markers are sized by their adjusted closeness centrality score (see below). Data via Opta.

Philippe Coutinho (10) was often a crucial cog in the network as he linked up with many of his team mates and the possessions he was involved with were often dangerous. His links with Sakho (17) and Moreno (18) appears to have been a fruitful avenue for attacks – this is an area we could examine in more detail via both data and video analysis if we were scouting Liverpool’s play. Over the whole season, Coutinho was easily the most crucial link in the team, which will come as no surprise to anyone who watched Liverpool last season.

Making the play

We can go further than players on a single team and compare across the entire league last season. To do this, I’ve calculated each players ‘closeness centrality‘ score or player influence score but scaled it according to how dangerous the possessions they were involved in were over the season. The rating is predominantly determined by how many possessions they are involved in, how well they link with team mates and the danger rating of the possessions they contribute to.

Yaya Touré leads the league by some distance due to him essentially being the crucial cog in the best attack in the league last season. Many of the players on the list aren’t too surprising, with a collection of Arsenal and Manchester City players high on the list plus the likes of Coutinho and Hazard also featuring.

The ability to effectively dictate play and provide a link for your team mates is likely desirable but the level of involvement a player has may be strongly governed by team tactics and their position on the field. One way around this is to control for the number of possessions a player is involved in to separate this out from the rating; Devin Pleuler made a similar adjustment in this Central Winger post.

Below are the top twenty players from last season according to this adjusted rating, which I’m going to refer to as an ‘influence rating’.

Top twenty players (minimum 1800 minutes) per the adjusted influence rating for the 2014/15 Premier League season. The number of completed passes each player made per 90 minutes is shown on the left. Data via Opta.

When accounting for their level of involvement, Mesut Özil rises to the top, narrowly ahead of Santi Cazorla and Yaya Touré. While players such as these don’t lead the league in terms of the most dangerous passes in open-play, they appear to be crucial conduits for their respective attacks. That might entail choosing the best options to facilitate attacks, making space for their team mates or playing a crucial line-breaking pass to open up a defence or all of the above and more.

There are some surprising names on the list, not least the Burnley duo of Danny Ings and George Boyd! Their level of involvement was very low (the lowest of those in the chart above) but when they were involved, Burnley created quite dangerous attacks and they linked well with the rest of the team. Burnley had a reasonably decent attack last season based on their underlying numbers but they massively under-performed when it came to actual goals scored. The question here is would this level of influence be maintained in a different setup and with greater involvement?

Ross Barkley is perhaps another surprising inclusion given his reputation outside of those who depict him as the latest saviour of English football. Looking at his passing chart and links, this possibly points to the model not accounting for crossing often being a less effective method of attack; his passing chart in the final third is biased towards passes to wide areas, which often then results in a cross into the box. Something for version 2.0 to explore. He was Everton’s attacking hub player, which perhaps helps to explain their lack of penetration in attack last season.

Conclusion

The above is just one example of breaking down my dangerous possession metric to the player level. As with all metrics, it could certainly be improved e.g. additional measures of quality of possession could be included and I’m aware that there are likely issues with team effects inflating or deflating certain players. Rating across all players isn’t completely fair, as there is an obvious bias towards attack-minded players, so I will look to break it down across player positions and roles.

Stay tuned for future developments.

Valuing Possession

Regular visitors will know that I’ve been working on some metrics in relation to possession and territory based on the difficulty of completing passes into various areas of the pitch. To recap, passes into dangerous areas are harder to complete, which isn’t particularly revelatory but by building some metrics around this we can assess how well teams move the ball into dangerous areas as well as how well they prevent their opponents from doing so. These metrics can also be broken down to the player level to see which players complete the most ‘dangerous’ passes.

Below is the current iteration of the pass danger rating model based on data from the 2014/15 Premier League season; working the ball into positions closer to the goal is rewarded with a larger rating, while passes made within a teams own half carry very little weight.

Map of the pass weighting model based on data from the English Premier League. Data via Opta.

Map of the pass weighting model based on data from the English Premier League. Data via Opta.

One particular issue with the Territorial-Possession Dominance (TPD) metric that I devised was that as well as having a crap name, the relationship with points and goal difference could have been better. The metric tended to over-rate teams who make a lot of passes in reasonably dangerous areas around the edge of the box but infrequently complete passes into the central zone of the penalty area. On the other side of the coin, it tended to under-rate more direct teams who don’t attack with sustained possession.

In order to account for this, I’ve calculated the danger rating by looking at attacks on a ‘possession’ basis i.e. by tracking individual chains of possession in open-play and looking at where they end. The end of the chain could be due to a number of reasons including shots, unsuccessful passes or a tackle by an opponent. Each possession is then assigned a danger rating based on the model in the figure above. Possessions which end deep into opponent territory will score more highly, while those that break down close to a team’s own goal are given little weight.

Conceptually, the model is similar to Daniel Altman’s non-shot based model (I think), although he views things through expected goals, whereas I started out looking at passing. You can find some of the details regarding the model here, plus a video of his presentation at the Opta Pro Analytics Forum is available here, which is well worth watching.

Danger Zone

The ratings for last season’s Premier League teams are shown below, with positive values meaning a team had more dangerous possessions than their opponents over the course of the season and vice versa for the negative values. Overall, the correlation between the metric and goal difference and points is pretty good (r-squared values of 0.76 and 0.77 respectively). This is considering open-play only, so it ignores set pieces and penalties, plus I omitted possessions made up of just one shot. The correlation with open-play goal difference is a little larger, so it appears to be an encouraging indicator of team strength.

Open-Play Possession Danger Rating for the 2014/15 English Premier League season. Data via Opta.

Open-Play Possession Danger Rating for the 2014/15 English Premier League season. Zero corresponds to a rating of 50%. Data via Opta.

The rating only takes into account the location of where the possession ends so there is plenty of scope for improvement e.g. throughball passes could carry more weight, counter-attacks could receive an increased danger rating, while moves featuring a cross might be down-weighted. Regardless of such improvements, these initial results are encouraging and are at a similar descriptive level to traditional shot ratios and expected goal models.

Arsenal are narrowly ahead of Manchester City here, as they make up a clear top-two which is strongly driven by their attacking play. Intriguingly, Manchester City’s rating was much greater (+7%) for possessions ending with a shot, while Arsenal’s was almost unchanged (-1%). Similarly to City, Chelsea’s rating for possessions ending with a shot was also greater (+4%)  than their rating for all possessions. I don’t know yet if this is a repeatable trait but it suggests Chelsea and City were more efficient at generating quality shots and limiting their opponents.

Manchester United sit narrowly ahead of Liverpool and Southampton and round out the top four, which was mainly driven by their league-leading defensive performance; few teams were able to get the ball into dangerous positions near their goal. Manchester United’s ability to keep their opponents at arms length has been a consistent trend from the territory-based numbers I’ve looked at.

Analytics anti-heroes Sunderland and a West Brom team managed by Tony Pulis for a large chunk of last season reside at the bottom of the table. Sunderland comfortably allowed the most dangerous possessions in the league last season.

Possessed

So, we’re left with yet another team strength metric to add to the analytics pile. The question is what does this add to our knowledge and how might we use it?

Analytics has generally based metrics around shots, which is sometimes not reflective of how we often experience the game from a chance creation point of view. The concept of creating a non-shot based chance isn’t a new one – the well worn cliché about a striker ‘fluffing a chance’ tells us that much but what analytics is striving to do is quantify these opportunities and hopefully do something useful with them. Basing the metric on all open-play possessions rather than just focusing on shots potentially opens up some interesting avenues for future research in terms of examining how teams attack and defend. Furthermore, using all possessions rather than those just ending with a shot increases our sample size and opens up the potential for new ways of assessing player contributions.

Looking at player contributions to these possessions will be the subject of my next post.

Liverpool Looking Up? EPL 2015/16 Preview

Originally published on StatsBomb.

After the sordid love affair that culminated in a strong title challenge in 2013/14, Liverpool barely cast a furtive glance at the Champions League places in 2014/15. Their underlying numbers over the whole season provided scant consolation either, with performance levels in line with a decent team lacking the quality usually associated with a top-four contender. Improvements in results and underlying performance will therefore be required to meet the club’s stated aim of Champions League football.

Progress before a fall

Before looking forward to the coming season, let’s start with a look back at Liverpool’s performance over recent seasons. Below is a graphic showing Liverpool’s underlying numbers over the past five seasons, courtesy of Paul Riley’s Expected Goal numbers.

Expected goal rank over the past 5 seasons of the English Premier League. Liverpool seasons highlighted in red.

Expected goal rank over the past 5 seasons of the English Premier League. Liverpool seasons highlighted in red.

From 2010/11 to 2012/13, there was steady progress with an impressive jump in 2013/14 to the third highest rating over the past five years. Paul’s model only evaluates shots on target, so Liverpool’s 2013/14 rating is potentially biased a little high given their unusual/unsustainable proportion of shots on target that year. However, the quality was clear, particularly in attack. Not to be outdone, 2014/15 saw another impressive jump but unfortunately the trajectory was in the opposite direction. Other metrics such as total shots ratio and shots on target ratio tell a similar story, although 2013/14 isn’t quite as impressive.

The less charitable among you may ascribe Liverpool’s trajectory with the presence and performance of one Luis Suárez; when joining in January 2010, Suárez was an erratic yet gifted performer who went on to become a genuine superstar before departing in the summer of 2014. Suárez’s attacking wizardry in 13/14 was remarkable and he served as a vital multiplier in the sides’ pinball style of play. Clearly he was a major loss but there were already reasons to suspect that some regression was due with or without him: Andrew Beasley wrote about the major and likely unsustainable role of set piece goals, while James Grayson and Colin Trainor highlighted the unusually favourable proportions of shots on target and blocked shots respectively during their title challenge. I wrote about how Liverpool’s penchant for early goals had led to an incredible amount of time spent winning over the season (a handy circumstance for a team so adept at counter-attacking), which may well have helped to explain some of their unusual numbers and that it was unlikely to be repeated.

These mitigating and potentially unsustainable factors notwithstanding, the dramatic fall in underlying performance, points (22 in all) and goals scored (an incredible 49 goal decline) is where Liverpool find themselves ahead of the coming season. Such a decline sees Brendan Rodgers go into this season under pressure to justify FSG’s backing of him over the summer, particularly with a fairly nightmarish run of away fixtures to start the season and the spectre of Jürgen Klopp on the horizon.

So, where do Liverpool need to improve this season?

Case for the defence

With the concession of six goals away at Stoke fresh in the memory, the narrative surrounding Liverpool’s defence is strong i.e. the defence is pretty horrible. Numbers paint a somewhat different story with Liverpool’s shots conceded (10.9 per game) standing as the joint-fifth lowest in the league last year according to statistics compiled by the Objective-Football website (rising to fourth lowest in open play). Shots on target were less good (3.8 per game and a rank of joint-seventh) although the margins are fairly small here. By Michael Caley’s and Paul Riley’s expected goal numbers, Liverpool ranked fourth and sixth respectively in expected goals against. Looking at how effective teams were at preventing their opponents from getting the ball into dangerous areas in open-play, my own numbers ranked Liverpool fifth best in the league.

It should be noted that analytics often has something of a blind spot when it comes to analysing defensive performances; metrics which typically work very well on the offensive side often work less well on the defensive side. Liverpool also tend to be a fairly dominant team and their opponents typically favour a deep defence and counter strategy against them, which will limit the number of chances they create.

One area where their numbers (courtesy of Objective-Football again) were noticeably poor was at set-pieces where they conceded on 11.6% of the shots by their opponents, which was 3rd worst in the league, compared to a league average conversion of 8.7%. Set-piece conversion rates are notoriously unsustainable year-on-year though, so some regression towards more normal conversion rates could potentially bring down Liverpool’s goal per game average compared to last season.

While Liverpool’s headline numbers were reasonable, their tendency to shoot themselves in the foot and concede some daft goals was impressive in its ineptitude at times. Culprits typically included combinations of Rodgers’ tactics, Dejan Lovren’s ‘whack a mole’ approach to defending and the embers of Steven Gerrard’s Liverpool career. The defensive structure of the team should be improved now that Gerrard no longer needs to be accommodated at the heart of midfield, while Glen Johnson’s prolonged audition for an extra role in the Walking Dead will continue at Stoke. Nathaniel Clyne should be a significant upgrade at full back, with youngsters Ilori and Gomez presently with the squad and aiming to compete for a first team role.

Broadly speaking though, Liverpool’s defensive numbers were reasonable but with room for improvement. Their numbers looked ok for a Champions League hopeful rather than a title challenger. A more mobile midfield should enhance the protection afforded to the central defence, however it should line up. Whether the individual errors were a bug and not a feature of this Liverpool team will likely determine how the narrative around the defence continues this year.

Under-powered attack

Liverpool’s decline in underlying performance in 2014/15 was driven by a significant drop-off in their attacking numbers. The loss of Suárez was compounded by Daniel Sturridge playing just 750 minutes in the league all season; Sturridge isn’t at the same level as Suárez (few are) but he does represent a truly elite forward and the alternatives at the club weren’t able to replace him.

The loss of Suárez and Sturridge meant that Coutinho and Sterling were now the principal conduits for Liverpool’s attack. Both performed admirably and were among the most dangerous attackers in the division. The figure below details Liverpool’s players according to the number of dangerous passes per 90 minutes played, which is related to my pass-danger rating score. In terms of volume, Coutinho and Sterling were way ahead of their teammates and both ranked in the top 15 in the league (minimum of 900 minutes played). James Milner actually ranked seventh by this metric, so he could well provide an additional source of creativity and link well with Liverpool’s forward players.

Dangerous passes per 90 minutes played metric for Liverpool players in 2014/15. Right hand side shows total number of completed passes per 90 minutes.

Dangerous passes per 90 minutes played metric for Liverpool players in 2014/15. Right hand side shows total number of completed passes per 90 minutes.

As good as Coutinho and Sterling were from a creative perspective, they did lag behind the truly elite players in the league by these metrics. As with many of Liverpool’s better players, you’re often left with the caveat of stating how good they are for their age. That’s not a criticism of the players themselves, merely a recognition of their overall standing relative to their peers.

What didn’t help was the lack of attacking contribution from Liverpool’s peak-age attacking players; Lallana’s contribution was decidedly average, Sturridge is obviously capable of making a stellar contribution but injuries curtailed him, while Balotelli certainly provided a high shot volume powered by a predilection for shooting from range but a potential dose of bad luck meant his goal-scoring record was well below expectation.

While there were clearly good elements to Liverpool’s attack, they were often left shooting from long range. According to numbers published by Michael Caley, Liverpool took more shots from outside the box than any other team last year and had the fourth highest proportion of shots from outside the box (48%). Unsurprisingly, they had the third lowest proportion of shots from the central region inside the penalty area (34%), which is the so-called ‘danger zone’ where shots are converted at much greater rates than wide in the box and outside the area. With their shot volumes being pretty good last season (third highest total shots and fourth highest shots on target), shifting the needle towards better quality chances would certainly improve Liverpool’s prospects. The question is where will that quality come from?

Bobby & Ben

With Sturridge not due back until the autumn coupled with his prior injury record, Liverpool moved to sign Christian Benteke as a frontline striker with youngsters Ings and Origi brought in to fill out the forward ranks. Roberto Firmino was added before Sterling’s departure but the expectation is that he will line-up in a similar role as the dynamic attacking midfielder/forward.

Firmino brings some impressive statistical pedigree with him: elite dribbler, dangerous passer, a tidy shot profile for a non-striker and stand-out tackling numbers for his position. If he can replicate his Bundesliga form then he should be a more than adequate replacement for Sterling, while also having the scope to develop over coming seasons.

Benteke brings a good but not great goal-scoring record, with his record in open-play being particularly average. Although there have been question marks regarding his stylistic fit within the team, Liverpool have seemingly been pursuing a physical forward to presumably act as a ‘reference point’ in their tactical system over the past few years; Diego Costa was a target in 2013, while Wilfred Bony was linked in 2014. Benteke brings that to the table alongside a more diverse range of skills than he is given credit for having been seemingly cast as an immobile lump of a centre forward by some.

Whether he has the necessary quality to improve this Liverpool team is the more pertinent question. From open-play, Benteke averages 2.2 shots per 90 minutes and 0.34 goals per 90 minutes over the past three seasons, which is essentially the average rate for a forward in the top European leagues. For comparison, Daniel Sturridge averages 4.0 shots per 90 minutes and 0.65 goals per 90 minutes over the same period. Granted, Sturridge has played for far greater attacking units than Aston Villa over that period but based on some analysis of strikers moving clubs that I’ve done, there is little evidence that shot and goal rates rise when moving to a higher quality team. Benteke does provide a major threat from set-pieces, which has been a productive source of goals for him but I would prefer to view these as an added extra on top of genuine quality in open-play, rather than a fig leaf.

Benteke will need to increase his contribution significantly if he is to cover for Sturridge over the coming season, otherwise Liverpool may find themselves in the good but not great attacking category again.

Conclusion

So where does all of the above leave Liverpool going into the season? Most of the underlying numbers for last season suggested that Chelsea, Manchester City and Arsenal were well ahead of the pack and I don’t see much prospect of one of them dropping out of the top four. Manchester United, Liverpool and Southampton made up the trailing group, with these three plus perhaps Tottenham in a battle to be the ‘best of the rest’ or ‘least crap’ and claim the coveted fourth place trophy.

When framed this way, Liverpool’s prospects look more viable, although fourth place looks like the ceiling at present unless the club procure some adamantium to alleviate Sturridge’s injury woes. While Liverpool currently operate outside the financial Goldilocks zone usually associated with a title challenge, they should have the quality to mount a concerted challenge for that Champions League spot in what could be a tight race. They did put together some impressive numbers during the 3-4-3 phase of last season that was in-line with those expected of a Champions League contender; replicating and sustaining that level of quality should be the aim for the team this coming season.

Prediction: 4-6th, most likely 5th.

P.S. Can Liverpool to be more fun this year? If you can’t be great, at least be fun.

Premier League Pass Masters

In this previous post, I combined territory and possession to create a Territorial-Possession Dominance (TPD) metric. The central basis for this metric is that it is more difficult to pass the ball into dangerous areas. Essentially teams that have the ball in areas closer to their opponent’s goal, while stopping their opponent moving the ball close to their own, will score more highly on this metric.

In the graphic below, I’ve looked at how the teams in the Premier League have been shaping up this year (data correct up to 24/04/15). The plot splits this performance on the offensive side (with the ball) and the defensive side (without the ball). For a frame of reference, league average is defined as a score of 100.

Broadly, these two terms show that teams who dominate territory with the ball also limit the amount of possession they concede close to their own goal. This makes sense given there is only one ball on the pitch, so pinning your opponent back in their half makes it more difficult to maintain possession in dangerous areas in return. Alternatively, teams may choose to sit back, soak up pressure and then aim to counter attack; this would yield a low rating offensively and a higher rating defensively.

Territorial-possession for and against for the 2014/15 English Premier League. A score of 100 denotes league average. Marker colour refers to Territorial-Possession Dominance. Data via Opta.

The top seven (plus Everton) tend to dominate territory and possession, while the bottom thirteen (minus Everton) are typically pinned back. Stoke City are somewhat peculiar, as they are below average on both scores,so while they limit their opponents, they seemingly struggle to manoeuvre the ball into dangerous areas themselves. Michael Caley’s expected goals numbers suggest that Everton have seemingly struggled to convert their territorial and possession dominance into an abundance of good quality chances; essentially they look pretty in-between both boxes.

Sunderland’s passivity is evident as they routinely saw their opponents pass the ball into dangerous areas; based on where their defensive actions occur and the league-leading number of shots from outside of the box they concede, the aim is to get men behind the ball and prevent good quality chances from being created. That is possibly a reasonable tactical system if you can combine that with swift counter-attacking and high quality chances but Poyet’s dismissal is indicative of how that worked out.

On the flip side, Manchester United rank lowest for territorial-possession against. Their system is designed to prevent their opponent’s from building pressure on their defense close to their own goal. Think of it as a system designed to prevent Phil Jones’ face from trending on Twitter. Of course, when the system breaks down and/or opposition skill breaks through, things look awful and high quality chances are conceded.

Finally, Manchester City clearly aren’t trying hard enough.

Passing maestros

The metric I’ve devised classifies each pass completed based on the destination of the pass, so it is relatively straight-forward to breakdown the metric by the player passing the ball. Below are the top twenty players this season ranked according to the average ‘danger’ of their passes (non-headed passes only, minimum 900 minutes played). I can also do this for players receiving the ball but I’ll leave that for another time.

Players who routinely complete passes into dangerous areas will score highly here, so there is an obvious bias towards forwards and attacking midfielders/wingers. Bias will also be introduced by team systems, which would be a good thing to examine in the future. I’ve also noted on the right-hand-side the number of passes each player completes per 90 minutes to give a sense of their involvement.

Some players, like Diafra Sakho and Jamie Vardy, are rarely involved but their passes are often dangerous. Others manage to combine a high-volume of passes with danger; PFA Player of the Year, Eden Hazard, is the standout here (very much a Sum 41 kind of footballer). The link-up skills of Sánchez and Agüero are also evident.

Pass Danger Rating for English Premier League players in the 2014/15 season. Numbers on right indicate number of completed passes played per 90 minutes by each player. Minimum of 900 minutes played. Data via Opta.

I quite like this as a metric, as the results aren’t always obvious; it is nice to have confirmatory metrics but informative metrics are potentially more valuable from an analytics point of view. For instance, the metric can quickly identify the dangerous passers for the opposition, who could then be targeted to reduce their influence. It can also be useful in identifying players who could possibly do more on your own team (*cough* Lallana *cough*). Finally, it’s a metric that could be used as a part of an analytics based scouting system. I’m hoping to develop this further, so watch this space.

Help me rondo

In my previous post, I looked at the relationship between controlling the pitch (territory) and the ball (possession). When looking at the final plot in that post, you might infer that ‘good’ teams are able to control both territory and possession, while ‘bad’ teams are dominated on both counts. There are also teams that dominate only one metric, which likely relates to their specific tactical make-up.

When I calculated the territory metric, I didn’t account for the volume of passes in each area of the pitch as I just wanted to see how things stacked up in a relative sense. Territory on its own has a pretty woeful relationship with things we care about like points (r2=0.27 for the 2013/14 EPL) and goal difference (r2=0.23 for the 2013/14 EPL).

However, maybe we can do better if we combine territory and possession into one metric.

To start with, I’ve plotted some heat maps (sorry) showing pass completion percentage based on the end point of the pass. The completion percentage is calculated by adding up all of the passes to a particular area on the pitch and comparing that to the number of passes that are successfully received. I’ve done this for the 2013/14 season for the English Premier League, La Liga and the Bundesliga.

As you would expect, passes directed to areas closer to the goal are completed at lower rates, while passes within a teams own half are completed routinely.

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Heat map of pass completion percentage based on the target of all passes in the 2013/14 English Premier League, La Liga and Bundesliga. Data via Opta.

What is interesting in the below plots is the contrast between England and Germany; in the attacking half of the pitch, pass completion is 5-10% lower in the Bundesliga than in the EPL. La Liga sits in-between for the most part but is similar to the Bundesliga within the penalty area. My hunch is that this is a result of the contrasting styles in these leagues:

  1. Defences often sit deeper in the EPL, particularly when compared to the Bundesliga, which results in their opponents completing passes more easily as they knock the ball around in front of the defence.
  2. German and Spanish teams tend to press more than their English counter-parts, which will make passing more difficult. In Germany, counter-pressing is particularly rife, which will make passing into the attacking midfield zone more challenging.

From the above information, I can construct a model* to judge the difficulty of a pass into each area of the pitch and given the differences between the leagues, I do this for each league separately.

I can then use this pass difficulty rating along with the frequency of passes into that location to put a value on how ‘dangerous’ a pass is e.g. a completed pass received on the penalty spot in your opponents penalty area would be rated more highly than one received by your own goalkeeper in his six-yard box.

Below is the resulting weighting system for each league. Passes that are received in-front of the goal within the six-yard box would have a rating close to one, while passes within your own half are given very little weighting as they are relatively easy to complete and are frequent.

There are slight differences between each league, with the largest differences residing in the central zone within the penalty area.

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Heat map of pass weighting model for the 2013/14 English Premier League, La Liga and Bundesliga. Data via Opta.

Using this pass weighting scheme, I can assign a score to each pass that a team completes, which ‘rewards’ them for completing more dangerous passes themselves and preventing their opponents from moving the ball into more dangerous areas. For example, a team that maintains possession in and around the opposition penalty area will increase their score. Similarly, if they also prevent their opponent from moving the ball into dangerous areas near their own penalty area, this will also be rewarded.

Below is how this Territorial-Possession Dominance (TPD) metric relates to goal difference. It is calculated by comparing the for and against figures as a ratio and I’ve expressed it as a percentage.

Broadly speaking, teams with a higher TPD have a better goal difference (overall r2=0.59) but this varies across the leagues. Unsurprisingly, Barcelona and Bayern Munich are the stand-out teams on this metric as they pin teams in and also prevent them from possessing the ball close to their own goal. Manchester City (the blue dot next to Real Madrid) had the highest TPD in the Premier League.

In Germany, the relationship is much stronger (r2=0.87), which is actually better than both Total Shot Ratio (TSR, r2=0.74) and Michael Caley’s expected goals figures (xGR, r2=0.80). A major caveat here though is that this is just one season in a league with only 18 teams and Bayern Munich’s domination certainly helps to strengthen the relationship.

The relationship is much weaker in Spain (r2=0.35) and is worse than both TSR (r2=0.54) and xGR (r2=0.77).  A lot of this is driven by the almost non-existent explanatory power of TPD when compared with goals conceded (r2=0.06). La Liga warrants further investigation.

England sits in-between (r2=0.69), which is on a par with TSR (r2=0.72). I don’t have xGR numbers for last season but I believe xGR is usually a few points higher than TSR in the Premier League.

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Relationship between goal difference per game and territorial-possession dominance for the 2013/14 English Premier League, La Liga and Bundesliga. Data via Opta.

The relationship between TPD and points (overall r2=0.56) is shown below and is broadly similar to goal difference. The main difference is that the strength of the relationship in Germany is weakened.

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Relationship between points per game and territorial-possession dominance for the 2013/14 English Premier League, La Liga and Bundesliga. Data via Opta.

Over the summer, I’ll return to these correlations in more detail when I have more data and the relationships are more robust. For now, the metric appears to be useful and I plan to improve it further. Also, I’ll be investigating what it can tell us about a teams style when combined with other metrics.

——————————————————————————————————————– *For those who are interested in the method, I calculated the relative distance of each pass from the centre of the opposition goal using the distance along the x-axis (the length of the pitch) and the angle relative to a centre line along the length of the pitch.

I then used logistic regression to calculate the probability of a pass being completed; passes are deemed either successful or unsuccessful, so logistic regression is ideal and avoids putting the passes into location buckets on the pitch.

I then weighted the resulting probability according to the frequency of passes received relative to the distance from the opposition goal-line. This gave me a ‘score’ for each pass, which I used to calculate the territory weighted possession for each team.

Germany vs Portugal: passing network analysis

Germany faced Portugal in their opening Group G match, with Germany winning 4-0 and Pepe being an idiot (surprise, surprise). Faced with the decision on which diminutive gifted midfielder to leave out of the starting eleven, Jogi Löw just went ahead and picked all of them. Furthermore, Germany’s best fullback, Phillip Lahm played centre midfield. Ronaldo was fit enough to start for Portugal.

Below are the passing networks for both Germany (left) and Portugal (right) based on data from Fifa.com. More information on how these are put together is available here in my previous posts on this subject. For Germany, I’ve not included the substitutes as they contributed little in this aspect. For Portugal, I included Eder who came on for the injured Hugo Almeida after 28 minutes.

Passing networks for the World Cup Group G match between Germany and Portugal at the Arena Fonte Nova, Salvador on the 16th June 2014. Only completed passes are shown. Darker and thicker arrows indicate more passes between each player. The player markers are sized according to their passing influence, the larger the marker, the greater their involvement. Click on the image for a larger view.

Bear in mind that the passing networks above are likely skewed by game state effects, with Germany leading and playing 11 vs 10 for a large proportion of the match.

Germany

Germany lined up with something like a 4-1-5-0 formation in the first half, with their full backs being relatively unadventurous, Phillip Lahm playing ahead of the centre backs with Sami Khedira running from deep and often beyond his attacking compatriots. Khedira was less aggressive in the second half with Germany three goals ahead and with a numerical advantage. In the graphic above, I’ve got them lined up in a 4-2-4ish formation based on a mixture of their average positions and making the plot look pretty. In reality, the side was very compact with the central defenders playing a high line and the attackers dropping off continually.

Lahm and Khedira provided a controlling influence for Germany, forming the link between the defence and attack. Höwedes and Boateng were also well involved in build-up play, although they had limited involvement in terms of direct creativity, with just one cross and no key passes between them.

The attacking quartet were all about fluid movement and passing links, as can be seen in the passing network above. Kroos was similarly influential to Lahm/Khedira but with a slightly higher position up the pitch. Özil and Götze were also heavily involved, while Müller was the least involved (unsurprisingly). The relative balance between the German play-makers meant that their attacks were not simply funnelled through one individual, which led to some lovely passing inter-changes and several high-quality shooting opportunities.

Portugal

Portugal’s passing network was dominated by their central midfielders but they struggled to involve their attacking players in dangerous areas. Ronaldo in particular saw relatively little involvement and the passes he did receive were often well away from the danger-zone. The one Portuguese attacker who was well-involved was Nani; unfortunately for Portugal, he put in a fairly terrible performance. Despite his involvement, Nani created no shooting opportunities for his team mates and put in a total of six crosses with none finding a fellow Portuguese. He did have three shots, with one on target. Sometimes a relatively high passing influence is a bad thing if the recipient wastes their involvement.

Portugal did look dangerous on the counter-attack prior to Pepe’s sending off but failed to really create a clear chance from these opportunities. Overall, Portugal’s passing network was too heavily weighted away from their (potentially) dangerous attacking players and when they did get the ball, they didn’t do enough with it.

Moving forward

Germany were impressive, although this was likely facilitated by Pepe’s indiscretion and the game being essentially over at half-time. The game conditions were certainly in their favour but they capitalised fully. If they can keep their gifted band of play-makers weaving their magic, then they will do well. They’ll need Müller to keep finishing their passing moves, while Mario Götze found himself in several promising shooting situations which may well yield goals on future occasions.

Conversely, Portugal were hampered by the match situation although they looked worryingly dependent on Ronaldo in attack, as noted by the imperious Michael Cox in his recap of day five. Furthermore, the USA likely won’t give them as much space to attack as Germany did. They’ll need to improve the passing links to their dangerous attackers if they are to have much joy at this tournament.

Newcastle United vs Liverpool: passing network analysis

Liverpool defeated Newcastle 6-0 at St James’ Park. Below is the passing network analysis for Liverpool split between the first 75 minutes of the match and the rest of the match up to full time. I focussed just on Liverpool here. More information on how these are put together is available here in my previous posts on this subject.

The reason I separated the networks into these two periods was that I noticed how Liverpool’s passing rate changed massively after Steven Gerrard was substituted and the fifth goal was scored. During the first 75 minutes, Liverpool attempted 323 passes with a success rate of 74% and a 45% share of possession. After this, Liverpool attempted 163 passes with an accuracy of 96% and a 60% share of possession. Liverpool attempted 34% of their passes in this closing period. Let’s see how this looks in terms of their passing network.

The positions of the players are loosely based on the formations played, although some creative license is employed for clarity. It is important to note that these are fixed positions, which will not always be representative of where a player passed/received the ball. The starting eleven is shown on the pitch for the first 75 minutes, with Borini replacing Gerrard in the second network.

Passing networks for Liverpool for the first and second halfs against Swansea City from the match at Anfield on the 17th February 2013. Only completed passes are shown. Darker and thicker arrows indicate more passes between each player. The player markers are sized according to their passing influence, the larger the marker, the greater their influence. Players with an * next to their name were substituted. Click on the image for a larger view.

Passing networks for Liverpool for the first 75 minutes and up to full time against Newcastle United from the match at St James’ Park on the 27th April 2013. Only completed passes are shown. Darker and thicker arrows indicate more passes between each player. The player markers are sized according to their passing influence, the larger the marker, the greater their influence. Click on the image for a larger view.

Liverpool’s passing was quite balanced for the first 75 minutes of the match, with a varied passing distribution. There was a stronger bias towards the right flank compared with the left flank as Gerrard drifted right to combine with Johnson and Downing. The passing influence scores were also evenly distributed across the whole team with Gerrard and Lucas being the top two. A contrast with some previous matches is the lack of strong links along the back line, which indicates less reliance on recycling of possession in deeper areas. Instead, Liverpool were seeking to move the ball forward more quickly and played the ball through the whole team.

He makes us happy

After Gerrard and Lucas, the next most influential player was Coutinho, who put in a wonderfully creative performance as the attacking fulcrum of the team. He linked well with all of Liverpool’s forward players and threaded several dangerous passes to his team-mates including an assist and a ‘second goal assist’ (defined as a pass to the goal assist creator) for the second goal according to EPL-Index. His creative exploits thus far have been hugely promising during his first 10 appearances.

Sterile domination

The final period of the match saw Liverpool really rack up the passing numbers as mentioned earlier. Clearly, this is easier to do when 5 or 6 goals clear but it is still potentially illustrative to see how this was accomplished. The main orchestrator’s of this were Lucas and Henderson who were 28/28 and 35/35 for passes attempted/completed during this period. Henderson was 21/24 from the first 75 minutes, so this was quite a rapid increase with his shift in role after Gerrard went off and the state of the game.

Your challenge should you wish to accept it

Admittedly Newcastle were very poor in this match but Liverpool took advantage to enact a severe thrashing. This was accomplished without Suárez, which leads to obvious (premature?) questions about whether his absence improved Liverpool’s overall balance and play. Assuming that Suárez doesn’t leave in the summer, one of Bredan Rodgers’ key tasks will be developing a system that gets the best out of the attacking talents of Suárez, Coutinho and Sturridge. It could be quite tasty if he manages to accomplish this.

Bayern Munich vs Barcelona: passing network analysis

Bayern Munich defeated Barcelona 4-0 with a dominant performance. The way both teams approached the game in terms of their passing was interesting and worth some additional analysis.

Much of the post-match discussion on TV focussed on Barcelona’s dominance of possession not being reflected in the final scoreline. According to UEFA, Barcelona had 63%, while WhoScored/Opta had it at 66%. However, Bayern were well ahead in terms of shots (15-4 in favour of Bayern, with a 7-1 advantage for on-target shots). It seems that whenever Barcelona lose, their possession statistics are trotted out as a stick to beat them with. Given that Barcelona have gone more than 300 games and close to half a decade since they last played a game with less than 50% possession, I very much doubt there is causality between their possession statistics and match results. Barcelona choose to play this way and it has certainly been successful. However, it is worth remembering that not all teams play the same way and the assumption that there is a single holy grail metric that can ‘explain’ winning football matches is probably a fool’s errand. Even if one does exist, it isn’t a match aggregated possession statistic.

Process, not outcome

In terms of passing, I’ve tried to look more at the process using network analysis to establish how teams pass the ball and which players are the most influential in passing terms in a given match, rather than focussing on a single statistic. Below is the passing network for the match. The positions of the players are loosely based on the formations played by the two teams, although some creative license is employed for clarity. It is important to note that these are fixed positions, which will not always be representative of where a player passed/received the ball. Only the starting eleven is shown as the substitutes had little impact in a passing sense.

Passing network for Bayern Munich and Barcelona from the Champions League match at the Allianz Arena on the 23rd April 2013. Only completed passes are shown. Darker and thicker arrows indicate more passes between each player. The player markers are sized according to their passing influence, the larger the marker, the greater their influence. The size and colour of the markers is relative to the players on their own team i.e. they are on different scales for each team. Only the starting eleven is shown. Click on the image for a larger view.

As might be expected, the contrast between the two teams is quite clear. Bayern focussed their passing down the flanks, with Ribery and Robben combining well with their respective full-backs. Neuer, Dante and Boateng fed the full-backs well to begin these passing transitions. Barcelona on the other hand engaged in their familiar multitude of passing triangles, although with a bias towards their right flank. There are a number of strong links although the somewhat uninspiring Bartra-Pique link was the strongest (23 passes).

Sterile domination

The issue for Barcelona was that their possession was largely in deeper areas, away from Bayern’s penalty area. This was neatly summed up by this tweet (including a graphic) by Albert Larcada:

While Barcelona’s passing network showed plenty of combinations in deeper areas, their more attacking players combined much less, with the links between Alexis, Messi and Pedro being relatively weak. In particular, the passes to Messi were low in number as he received just 7 passes combined from Iniesta (3), Pedro (2) and Alexis (2). Messi had much stronger links with Xavi (received 20 passes) and Alves (received 19 passes) although I suspect many of these were in deeper areasWhile, Barcelona’s midfield three exerted their usual influence, the next most influential players were Pique and Bartra. This is a stark comparison with the home match against AC Milan, where Messi was the most influential player after the midfield trio.

Bayern did a great job of limiting Messi’s influence, although his injury likely contributed also.

Avoid the puddle

Schweinsteiger was the most influential player for Bayern, linking well with Dante, Alaba and Ribery. After the centre-backs, Bayern’s next most influential players were Robben and Ribery who counter-attacked superbly, with excellent support from their full-backs. As discussed by Zonal Marking, Bayern preyed on Barcelona’s weakness on the counter-attack with speedy breaks down the flanks.

Bayern were incredibly effective and deservedly won the match and very likely the tie.

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Passing matrices from Uefa.com press kits.