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Football the English Way

For as long as I can remember the British football pundits, media and commentators have talked about how the English game was faster / more physical / had less space (delete as appropriate) than the football that was played far away in a land named Europe.
I have often wondered how they arrived at that conclusion.

The hard pressing, high line tactic that has started to make its way into England in recent years has its roots firmly established in Europe.  All other things being equal, this gradual acceptance in England of the hard press should therefore mean that when in possession, players in England should have more time on the ball than their foreign counterparts.

In this piece I’m going to use my Expected Goal data to demonstrate that it really is much tougher to score from any given shot in the Premier League than in any of the other Big 4 European leagues.  This assertion is based on the 2012/13 season – it is limited to last season due to a lack of prior data.

agb

Can we demonstrate that it is more difficult to score in England?

In order for the numbers to “prove” that it is more difficult to score in the Premier League we are going to have to make just one assumption. I am fine with this as I think it is a reasonable assumption to make, but I’ll let you decide.

The one assumption required for these numbers to hang together is that “Strikers in the EPL are on average no worse than those in the other Big 4 leagues”.

I certainly think this is the case.  For every Bale and Ronaldo that have left the EPL at the height of their powers we have an Aguero, Negredo, Navas, Soldado to replace them.  The money that permeates throughout the Premier League means that this assumption is perfectly valid in my opinion.  Remember, the quality of the strikers doesn’t need to be better than the other leagues, just no worse on average.  On this basis I think we are OK to proceed.

Regular readers of my pieces will know that Constantinos Chappas and I have developed a model that assigns a goal probability (ExpG) for each shot.  The probability is based on the location, the type of shot and a few other factors, and was developed using shot information from across the 5 leagues.

The summary ExpG, shots and goals table for 2012/13 for the Big 5 leagues is shown below:

[table id=29 /]

The ExpG values are a work in progress – this explains why I now have the EPL at 84% efficiency (Goals / ExpG) whereas I had mentioned 90% in a previous article – as we tinker and fine tune them.  Note that Own Goals are excluded from the goals totals shown above.

For the 2012/13 season, the quality of the average chance attempted was marginally higher in England than in the other leagues at 0.114 Expected goals per shot.  Germany and Spain followed closely behind at a clip of 0.11 goals per shot.

However, look at the Goals / Shot ratio.
The Premier League only actually recorded 0.096 of a goal per shot, which is at just 84% of our expected rate.  On the other hand, the Bundesliga teams recorded 0.112 goals per shot.  So from what appeared to be less productive shots the German teams managed to score much more goals per shot than the Premier League and indeed, in absolute terms, more goals than our model had expected them to score.
Ligue 1 is also interesting.  This league is notoriously low scoring, but this is due as much to the lack of shooting (less than 24 shots on average per game) as it is the average shot quality.

Please keep in mind that for this exercise we are not interested in the total number of goals or shots achieved in each league.  We’re interested in the average shot quality in each league and then the subsequent conversion of those average shots as I look at how our ExpG efficiency, which is an objective measure, varies by league.

wellb

Possible explanations for the EPL under achievement

I can come up with a few reasons why our model has seen goals in England converted at just 84% of the rate that we had expected:

  1. Defensive Pressure
  2. Better standard of Goal Keeping than in other leagues
  3. Our model, although good, is missing other certain ingredients to capture exactly the rate that any given chance is converted
  4. Chance or random variance

Most of those possible explanations are fairly wide ranging, and ones that I’m not sure how to tackle at this stage.  But using an idea that Sam Green posted in an Opta blog in 2012 I have come up with a method of evaluating the amount of the shortfall in shot conversion that is due to defensive pressure, and it’s this that I want to investigate.

Introducing ExpG2

Up until this point, our Expected Goal model looked exclusively at the factors present at the point that the shot was struck.
We have used a similar framework to create an Expected Goal model which is based on where the shot was aimed for, and I’m using this article to introduce this metric.

In order to differentiate these two different Expected Goal values we will now refer to the expected goal probability at the point the shot was taken as ExpG1 and the value after the shot has been taken as ExpG2.

A shot that is off target or blocked has an ExpG2 value of zero as those shots have no chance of resulting directly in a goal, whereas a shot that is arrowed right for the very top corner will have a high ExpG2 value as the likelihood of a goal is strong.  An extreme example would be a penalty that is aimed at the top corner; such a shot would have an ExpG2 value of approx 0.96 with an ExpG1 value of approx 0.75.

ExpG2 values

Let’s have a look at what the ExpG2 values looked like for each of the 5 leagues last season, and most importantly how they compare with their respective ExpG1 figures.

[table id=30 /]

I’m ignoring the actual goals scored for the purposes of this exercise, and instead am concentrating on the differences between the ExpG1 and ExpG2 values for each league.
For four of the leagues the differences between the two sets of values are small, at 2% or less.  But the difference between the ExpG1 and ExpG2 values for the Premier League last season are extremely significant in comparison at 10 percentage points.

Let me step you through exactly what this means, and the significance of this.

Looking at the situation at the point when the shots were struck (ExpG1) our model had expected to see 1201 goals in the Premier League last season.
Here’s the important bit.  When we then take account of where the shot was aimed for the expected total goals dramatically reduce to 1083.  Remember that the other four leagues showed comparatively little movement between the two measures.  This suggests that, on average, the other four leagues all exhibited similar tendencies on average in terms of the change in probability of a shot being scored after it has been struck compared to before the shot took place.  But for some reason, the English Premier League reacted totally differently.

Let’s now remind ourselves of the assumption that I made earlier in this article.
If we assume that the quality of the average striker in the Premier League is no worse than the average of those appearing in the other four leagues then the low Expected Goals total that has been calculated after the shots have been struck can only be due to defensive pressure.  As we’re happy that EPL players are no worse at shooting, and we have normalised the quality of the shots, there is no other reason to explain why such a large proportion of shots are blocked, miss the target or are aimed towards the centre of the goal.  This same amount of defensive pressure simply seems not to be present in other leagues.

As we have normalised for shot location and are ignoring whether the keeper actually saves the shot or not, we are left with the defensive pressure as the only remaining explanation for the large drop in goal expectation in the EPL between ExpG1 and ExpG2.

In my opinion it’s not important that we break down the reasons for this low ExpG2 totals between missed shots and blocked shots.  It’s enough to know that this heavy defensive pressure insures that the probability of a goal being scored in England from any given shot is much lower than our original model predicted, and indeed lower than in any of the other main European leagues.

Due to the lack of proper defensive measures we were always aware of the fact that our model didn’t take into account defensive pressure, but for the first time thanks to the introduction of the ExpG2 metric we can demonstrate the impact of defensive pressure that is epplied in the Premier League.

I am aware that this conclusion is based on just one season of data, but due to the size of the difference in the EPL, the defensive styles that tend to be played in England and the fact that there were almost 50,000 shots in this sample I would be confident that this phenomenon will hold true in other seasons.

Why Go To All That Bother?

Having done the work to demonstrate this, I now find myself asking if I needed to go to so much work in proving something that summary stats could have told us.

For example, Germany, Spain and France all had more than 34% of their shots on target last season; it was just over 31% in England.  This alone tells us that defensive pressure was greater, right?

Likewise, only 9.6% of all shots were scored in the EPL last season compared to 11.1% in the Bundesliga, 10.7% in Spain and 10.2% in the traditionally low scoring Ligue 1.  Again, I could have just used those stats and said “Due to lower percentage of shots on target and goals I conclude that there is greater pressure on attackers in England than anywhere else”, right?

However, although that would have been a short cut it might not have been correct.  The difference in shot on target percentage could have been due to shot locations, ie on average EPL shots were attempted from less advantageous shooting positions, alternatively the lower scoring percentage could have been due to the same reason combined with better performances from goalkeepers in the English league.

This detailed analysis has ruled both of those possible explanations out – hence why I feel it was required in order for me to be able to definitively conclude that the pressure exerted on the player shooting is at a much higher level in the Premier League than in other leagues.

Quantifying the Impact

Over the 380 game 2012/13 EPL season the Expected Goals fell from 1201 to 1083 on the ExpG1 and ExpG2 measures respectively.  This amounts to 0.31 goals per game, or just over 1% for each shot as there was an average of 28 shots per game last season.

At this point we reach the take away message from this piece:
Any specific shot in the EPL is scored at a rate of 1% less than the other four European leagues due to the pressure applied to the shooter, or due to other general defensive pressure

A 1% reduction in scoring per shot doesn’t sound like a huge amount, but when shots are only scored at an average rate of approximately 10%, that extra defensive pressure soon makes a difference to the number of goals that are actually scored.

Reasons for the Phenomenon

The central finding in this piece may come as a surprise to many, and indeed will be contested by quite a few, as conventional wisdom would hold that players in the continental leagues have less time on the ball due to the high pressing game that would be prominent in those leagues.

In fact only yesterday, a German based reader made this exact point in a comment in relation to an article where I made the point that our ExpG1 model over-estimated the number of goals that should have been scored in the Premier League:

You´re saying that there is a lot more defensive pressure in the PL than in other leagues e.g. the Bundesliga or Primera Division or even League 1. Well I don´t think that’s true. When Ozil moved to Arsenal, Fabregas said Ozil will enjoy PL because of the space OMs get in the PL. Then Ligue 1 is considered the league with less goals than other leagues. Furthermore the defensive compactness is definitely higher in the PD and the Bundesliga than in the PL. The athleticism may be higher in the PL but as our teams had to learn last year that doesn’t cover the fact that they are almost always split in two parts (an offensive and a defensive one) whereas other teams such as Dortmund, Valencia, Donezk and of course Bayern are defending with 11 men (even barca is defending with 10) and attack with 11.

I would suggest that although the hard press, high defensive line used in Europe certainly reduces space in the middle third of the pitch and leaves it more difficult for teams to be in control of the ball, once those defensive lines are breached the attackers are then faced with easier scoring chances.  The defences are not as well set on the edge of the box and there certainly won’t be as many bodies between the striker and the goal.
A perfect example of this was AVB during his time at Chelsea.  He attempted to play the high defensive line, perhaps his players weren’t ready for it, but once that line was breached they were powerless to prevent the opposition converting the chances they created.

  • Toshack

    Colin,

    Very interesting indeed! Some quick thoughts (could be entirely wrong):

    So generally playing a ”low” defensive line would make it harder to score?
    And would normally mean that the entire team plays “lower”?
    Which would mean a bit more emphasis on defence rather than attack?
    And result in lower amount of goals scored overall?
    Is there any logic to that?

    I think the general view (too simplistic?) is that there are (or has been) more good teams in the PL than in other big leagues (top four or six vs. top two) where there seems to be only a few top contenders for the title. Is this true and if so, could it have an effect here? Thinking more high quality teams in a league – higher amount of high quality defenders – more defensive pressure on forwards.

    Or is it that the “old” English combative game still exists to a degree and in general makes it harder to score compared to the other leagues?

    If you could measure ball tempo across the leagues– could this help explain (either way)?

    Or is there a difference in the number of dispossessions in the final third between the leagues – affecting the quality of the goal scoring chance?

    Sorry to be rambling on – just thinking out aloud…
    //Peter

    • Colin Trainor

      Toshack,
      I think the assumptions at the start of your piece are probably correct. That is why EPL has less goals than Budesliga and why the likes of Stoke have never been high goal scorers.

      I wanted to keep this article fairly simple (the subject matter was already complex) hence I didn’t complicate matters by introducing anything else or trying to provide explanations for my findings.

      • Toshack

        Cheers Colin,
        I see Dom had about the same conclusions.
        Sorry if my rambling ran off in too many directions. Just tried to pick my own brain while I was online.
        Now back to the work that pays my bills.
        I think you know, but still like to mention how much I have learned since StatsBomb started. Fantastic work.
        //Peter

  • Dom L.

    Hey Colin,
    again I love the way you reason. 🙂
    I totally agree with you: when you press high up the pitch, the scoring oppurtinities become much better for yourself (because you´re way closer to the opponents goal) and and for the opponent (because if you breach the first line, there are less men inbetween you and the goal). This leads to a higher ExG1 in continental Europe. We found (you did) the missing 10%! 🙂

    Dom

    PS.: Yeah you were right, I loved the article 😀

    • Colin Trainor

      Dom,
      Hopefully you can see why I didn’t write you much of a reply yesterday. Thought there was no point in repeating myself!!

      Glad you enjoy my articles and thought processes.
      Cheers

  • Egil

    Great article!
    I am wondering about the impact of headed shots:
    Firstly i assume there are more headed shots attempts in the PM than in other leagues?
    Secondly that headed shots are generally less accurate than normal strikes (not on target or not placed that good).
    Third that there are less power on the ball with headed strikes.
    I am thinking that while headed shots are taken in prime locations (with an attributed high ExpG-rate), they in reality have a lower expected goal rate than the potential normal shots taken instead in the other leagues. Both because they are more often not on target (?), and also that they are easier to save (because of less pace on the ball). They therefore pollute your model as shots taken in prime locations, but in reality with a lower chance of scoring.

    Do you think I am right in my assumptions, and do your model possibly take this into calculation (i looked for the original article introducing the ExpG to reread, but could not find it)?
    If your model do not take this into consideration, do you have any thoughts?

    • Colin Trainor

      Egil,
      Firstly, thanks for the praise. I’m just glad that you enjoyed reading it.
      You are correct that headers are from closer range than shots, and also that they are scored less often (http://statsbomb.com/2013/07/how-do-headers-compare-to-shots/).

      What you are missing, and that’s probably because I haven’t been very specific in this regard, is that our ExpG model is not purely a location based model. It takes into account the fact that a header will have a lower conversion rate than a shot taken from the exact same location. So, just because a shot is taken from a Prime location doesn’t mean that it will have a high ExpG value.

      I trust the above answers the questions that you posed.

  • Rahat

    Hello Colin,
    I must first of all congratulate you on what is a remarkably detailed article which I’m sure must have taken you a tremendous amount of effort to compile. i must also apologize for not going through this analysis in much detail as I would have liked.
    However i do believe i have understood the conclusions you are trying to make and wish to point out that i disagree.
    1. I know that you have mentioned that taking only one season’s data should not be a fallacy because of the size of the data involved , however I cannot in any way agree with that. Studying analysis and statistics of a full 380 game season can be remarkably complex and every different year will have so many changes to statistics that we cannot possibly ignore them. To justify only taking a year’s data for a study otherwise so in depth and scientific cannot seem to be anything but strange. i can only imagine that your reasons for not taking say a 5 year period would be because of the difficulty and complexity of studying 5 years of data because I cannot think of any other reason that a study so complex would have been over a longer time period so as to lend more credibility to it.

    2. “The one assumption required for these numbers to hang together is that “Strikers in the EPL are on average no worse than those in the other Big 4 leagues”
    First of all aren’t we studying the numbers of all goals that were scored in the league? As far as i’m aware these numbers aren’t exclusively related to strikers but to all the goals scored in the league (by players of different positions) So by just assuming the EPL has as good strikers as the other leagues isn’t comprehensive enough. Although i’m not sure of the numbers i know that a huge percentage of goals are scored through non-forwards throughout the course of a season.
    Also continuing from earlier, while i do agree the Foreign players in the premier league are of a similar or perhaps even superior level to those abroad (on an average), i also believe that the English players are of an inferior level to those produced by the likes of Spain, Italy and Germany. I think the comprehensive performances of their national teams will back me up there. Also I do not think there is any doubt that these nations produce players with more technical football. More cultured players , compared to the English players who rely on speed,strength etc.
    I do hope that the recent performances of the English national team and more importantly their style of play will confirm this.
    So therefore if the English players are inferior technically to their Spanish German and Italian counterparts doesn’t that increase their chances of being less lethal finishers? For me it simply has to and can only severely hamper the principal assumption that you have based this study on.

    They are many other points that I would like to make but i feel I should have a more detailed look at your analysis which i hope to do in the near future. Even though I disagree with you I do appreciate the efforts you made to compile this analysis and it is thoroughly commendable 🙂

    • Colin Trainor

      Rahat,
      Thanks for taking the time to leave such a detailed comment.

      In answer to the questions you posed:

      1 – Unfortunately I do not have access to the data that is required before last season. So it was either base the conclusions on one season, or else write nothing.
      Which course of action should I have steered?

      2 – Yes, you are correct. Use of the term “striker” was a short hand measure to refer to all players who took shots.

      As regards the assumption I’m making, you’re missing the fact that we are not talking about English players, but rather EPL players. SO this includes Van Persie, Soldado, Chicarito and Benteke etc
      With the money that is in the EPL, do you seriously think that the lower level of “bad” shots in the awful Ligue 1 compared to the EPL is due to the skill of the players instead of defensive pressure?

      The English National team argument is a red herring as most EPL teams tend to have more starting “foreigners” than Englishmen on them.

      • Rahat

        Hello Colin .

        1. All right. That makes sense. And I do appreciate the effort you’ve put in by publishing this study anyway even though I disagree 🙂
        2. Yes I’m glad you agree on the strikers point.
        As far as my assumption is concerned , Yes the EPL does without doubt contain a plethora of foreign players and we can only see the numbers increasing. However it should also not be forgotten that more than 30% of the players are still English. Obviously the most players on the premier league of any nationality are still England players. So in a study 30% of players that are technically inferior cannot possibly be ignored.
        Yes as time goes on the money in the EPL is getting even more foreigners in. For ex this season some quality foreign strikers have come in , even for some of the lower or mid table teams. Osvaldo , Bony , etc , the list goes on. And i do believe that as the english players go down , the scoring rates will reach par with the other TOP leagues.

        Also you mentioned Ligue 1 , as for that there is no comparison. I do consider that despite two mega rich clubs having entered the fray the French League still lacks quality and it is definitely harder to score in the PL than the Ligue 1. But haven”t we known that top scorers in Ligue 1 and say the Dutch league have always found it harder to replicate their scoring rates in the PL,La Liga and Serie A?

  • Rahat

    Also Colin, I just had a slightly better look at your analysis.
    Again I will mention that you have made a fantastic effort to try and break this down scientifically I think you’ve left too many other factors. I’ve always thought of compiling my own studies on similar themes but due to the number of variables i think I would have to involve i have found the task to be too cumbersome. But it’s important that we don’t derive conclusions from limited analysis. (thorough yes in your case,but in the whole picture still limited).
    So your conclusion is that it is harder to score in the PL. you’ve tried to derive this conclusion from shots converted in a very detailed way. However you’re forgetting several other factors. Football in open play just isn’t that simple. We’re not talking about a penalty shootout. when we talk about it being ‘harder’ to score goals, there have to be so many factors involved. We’re talking about scoring goals from open play here , and it isn’t always as simple as lumping the ball forward and getting a shot in.
    When we talk about it being harder to score we have to factor in so many things. They’re teams that monopolize possession and hence when the other team get the ball after a long period of time and have to act quickly they often behave erratically/take erratic shots. Example Spain at World Cup 2010. Look at the number of 1-0 wins they got. This Spanish team might not after a point of time been the most appealing to watch , however they hardly gave the ball away and hence made it harder for the opposition to get a sniff at goal.
    Then they’re cases like Chelsea’s champions league winning run. They conceded a plethora of shots at the goal right through the tournament. Yet they were lauded for their defense. Players like Messi , Robben etc all seemed to have off days. If you look at Bayern and Barca’s shot conversion against them it would be quite less. Does that mean Chelsea were hard to sccore against? In my opinion no not really, they had a huge slice of luck. I think everyone has recognized that.
    Yes i do know these are a few matches and we’re talking about a league in question.. But I’m merely trying to point a few anomaly’s out to you. About how being harder to score against is about so many things.
    Then of course they’re amazing defending teams. Teams that don’t even let you get a shot in from a good area. They keep you out of their box and frustrate you and hence force you to undertake wayward shooting.
    sometimes also they hardly let you gave a shot away at all.
    when teams like Bayern and Barca monopolize possession they hardly let you get shots away at all. Say Beyern play Stoke in a match. Bayern get 30 shots on goal,25 on target and they score 7 goals.
    Stoke get one shot on goal , on on target and a goal from that. Does that mean Bayern were easier to score against?

    Also then they’re other factors like from my thorough experience of having seen the Serie A, La Liga and the Premier League passionately for years now I enjoy all the 3 leagues for what they are. they do have certain factors that distinguish them. The premier league is fast paced in a sense, less technical (Though that is gradually changing with the foreign player AND manager influx) , more long balls , etc. La Liga is slightly slower (build up play) , but more technical , more skilled. Teams build from the back and when they reach the goal they get in good positions more often than not (and subsequently perhaps their shooting is better, apart from them being technically better as i already mentioned).
    Serie A is again more technical , more tactical, it’s quite clear by say the no. of overhead kicks that are attempted and scored or extraordinary acrobatic goals etc. Again similar to La Liga but more tactical, maybe a little less technical. (Spain have the best players in the world right now).
    So I think this has a significant impact on your statistics as well.

    All in all i think though a remarkably detailed analysis I think you’ve done a good job and got interesting results. But deriving any conclusion out of these, having left out SO many factors is naive.

    • Colin Trainor

      So in the absence of complete perfect information we should do nothing?

      That’ll really advance the cause and understanding of analytics in football.

      I have used league averages here, so there is no need to understand in the most granular detail how each team play. I am not attempting to model the intricacies of each team’s system.

      • Rahat

        It isn’t about doing nothing. I have already stated several times that this article has been a colossal analysis which I do respect.
        However if you intend to derive fixed conclusions , there a lot more factors to consider. So it’s not even about having perfect information.
        As for the role of analytics in football , their role is growing tremendously in football. Sites like whoscored.com are reasonably thorough and are picking up. However it is still hard to make conclusions in football based on certain statistics alone.

      • Rahat

        Also understanding how teams play cannot be anything but imperative.
        If we analyze La Liga and compare it to the Premier League the La liga had more passes than the PL throughout the year. Does that mean they are better at passing? (Well yes they might well be) But no not necessarily No. Does it mean they prefer passing? Yes. Why? Because that is the philosophy for most La Liga teams.

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