Monthly Archives: October 2012

Premier League 2011-12: Player Impacts – discussion

In previous posts I have tested different ways of rating players using Opta data to mark out key fields for each major position which correlate positively to points.  The summary of these reviews can be read here.

What troubled me about some of the findings in this process was the underperformance of some high-profile players whose strengths were clearly not rewarded by the analysis. For example, Ashley Cole, Theo Walcott, and even Fabricio Coloccini – who actually made the PFA Team of the Year last season. Although I’m pretty keen to separate subjective opinion from raw data analysis, in particular the presence of Coloccini in the PFA Team of the Year – voted for by fellow professionals – cannot be disregarded lightly. Not to mention his superb performance at the weekend!

So in this series of posts I have published another ‘view’ of footballers – this time looking at team performance in the league with and without a particular player in the starting line-up. This can be used as a simple indicator regarding which players’ presence helps/detracts from their team. I used Tableau Public for the first time for this, and had some teething issues attaching my graphs/tables, so they are shown in separate posts below.

Method

I calculated the average points gained, team goals scored and team goals conceded for every team and player and compared this to the team averages without that player in the starting line-up. Of course, those who started every game don’t have a ‘without’ average so I removed players who started every game. In addition, I took out players who started fewer than 4 games, and players who started more than 34 games. I did this on a whim after I saw that Robin van Persie had a negative impact to Arsenal’s points average – this happened because he started 37 games for Arsenal last season, and in the 1 game he didn’t start Arsenal won against Stoke. This annoyingly made Arsenal’s points average without RVP as 3pts per game, which is a bit ridiculous when he came off the bench and scored 2 in that game anyway! Players with 1 start had a similar problem, as the result of that game determined their impact. That example serves a purpose in explaining the limitations of a data table like the one below, even though the bias is reduced by increasing the min/max number of starts to 4 and 34. Of course if a player started in 34 games but the 4 he missed were away visits to Man City, Man Utd, Arsenal and Spurs then again his points average is more likely than not to be a little too high.

All the impacts below need to be taken with a pinch of salt but information is power, and I think this review is complementary to my previous player analyses and will help to give a better profile of players and their contribution to team performance. Incidentally, in this review Coloccini didn’t qualify because he started 35 games last season.

Hopefully, the tables/graphs are self-explanatory, but here are some highlights:

  • Adebayor for Spurs had the biggest positive effect on points for any team, followed by Arteta for Arsenal
  • Theo Walcott and Ashley Cole both had a strong positive effect for Arsenal and Chelsea respectively despite the poor stats analysis rating in previous posts
  • Notable ‘unlucky mascots’ for their teams were Berbatov for Man U and Ramsey and Arshavin for Arsenal
  • Swansea had a comparatively short range of differences between their players, which shows not only that they were able to field a remarkably consistent team for much of the season, but also perhaps indicates that no matter who was in the starting line-up, the player positions and tactics were relatively easy to substitute
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Premier League 2011-12: Player Impacts – average points

The below graph, created using Tableau, shows the difference between points earned last season with that player in the starting line-up, vs points earned without (positive is good!) sorted by team.

Qualifying players were in a team’s starting line-up between 4 and 34 times to create a ‘sensible’ average points difference. For more information on the methodology click here.

An interactive version of the graph is available at the following link:

http://public.tableausoftware.com/views/EPL2011-12GlobalPlayerImpact/AvgPointsdifference?:embed=y

Premier League 2011-12: Player Impacts – goals for & conceded

I used Tableau to create the following graph of the positive/negative difference relating to goals for/against based on team averages with/without that player in the starting line-up that season.

Qualifying players were in a team’s starting line-up between 4 and 34 times to create a ‘sensible’ average difference. For more information on the methodology click here.

Use the version linked to below and hover over data points to see which player each star represents. NB. positive numbers are good for both goals for and goals conceded.

http://public.tableausoftware.com/views/EPL2011-12GlobalPlayerImpact/GoalsForvsCon?:embed=y

Premier League 2011-12: Player Impacts – data

Below is the full table of data, also viewable in Tableau Public at the following link:

http://public.tableausoftware.com/views/EPL2011-12GlobalPlayerImpact/Data?:embed=y

It’s not that easy to read the column headings but it’s basically team points with, team points without, difference – then the same order for goals for followed by goals against then a final goal difference average.

For the goals conceded difference I deducted team goals conceded without from team goals conceded with so that positive numbers are desirable – hence goal difference became goals for diff + goals conceded diff.

Qualifying players were in a team’s starting line-up between 4 and 34 times to create a ‘sensible’ average points difference. For more information on the methodology click here.

Premier League 2011-12: Stat attack

In this post I will publish some notable statistics and some charts from last season’s premier league. For example, did you know that there were 1066 goals scored last season, an average of 2.81 goals per game? And yet the number of big chances, as defined by Opta, averaged 3.58 per game.

Below is a chart illustrating some of the most signifcant ‘types’ of goals scored last season in proportion to their average frequency (there is some overlap):

Most of the other charts should be pretty self-explanatory:

Frequency per game:

Successful Unsuccessful Total
Dribbles 12.99 16.48 29.47
Short passes 619.89 124.59 744.48
Long passes 60.56 49.24 109.80
Corners 3.07 6.15 9.22

The next chart identifies how teams fared from direct free kicks throughout the season. 5 teams didn’t manage a single direct free-kick goal last season, but it was not for the want of trying, as Chelsea had 38 attempts with no success! Compare this to Sunderland, the most prolific scorers from direct free-kicks, who converted 5 of their 19 (success rate of 26.7%) with contributions from McClean, Gardner and Larsson (3).

Stacked points chart, home and away.  Only 3 teams: Bolton, WBA and Wolves won more points away from home than at home.

The next chart breaks down the number of shots per team, in order of the final league table positions. Just looking at the table by eye, you can see a trend between league position and number of shots. But there are some exceptions, such as Newcastle and Stoke, whose league position belies the trend in number of shots taken.

The last chart I will publish in this post shows the frequency and success rate of headed shots per team.  We can use this to establish which teams tended to use the aerial threat of their attackers more/less than average. Here it is clear that Stoke, Wolves and Liverpool created the most headed shots, perhaps due to an emphasis on crossing the ball from wide positions.

Premier League 2011-12: ‘Dream Team’

So with my position reviews now complete, I have a few points to make about the processes I have tested and what can be learnt. What will be more interesting to some readers is the fact that I can now also publish an alternative ‘Dream Team’ for last season based on my bespoke analysis.

All of the data analysed in these position reviews considered players who had played a total of more than 1000mins from a place in the starting line-up – with the one exception made for central attacking midfielders (for whom the limit was 500mins). As a result, players who made a habit of substitute appearances or a positive (or negative) impact from the bench – Theo Walcott springs to mind here – may not be considered fairly. In addition, players who were injured or out of favour for a significant proportion of the season may have shown themselves to be truly important when they did play but again didn’t qualify for my lists – perhaps for example Carlos Tevez, Hatem Ben Arfa and Nemanja Vidic.

In addition, I tested different weighting methodologies for each position review. The weightings used are obviously essential to the the final tables by which players are ranked and it should be noted that very different lists can be easily calculated with a few tweaks to the model. This is not intended to be a definitive ‘who is best’ rating but rather a simple test of how players can be compared to one another with an eye on correlations to wins, draws and losses.

Lastly, one season does not make a great player and the game evolves from year to year. As a result, we can’t make any concrete conclusions from 1 season’s worth of data. The availability of this data has certainly encouraged me to seek out more where possible – of course, the bigger the sample size, the better the chances of making a definitive conclusion.

The key general qualities I found for each position are noted below:

Goalkeepers with a high proportion of saves to shots, good passing accuracy and low error frequency are the qualities that seemed most important for this position last season. No surprises there. Looking back at my review, and influenced by recent discussions by other bloggers regarding keeper behaviour, we can imagine that all of these ratios are quite dependent on the team in which the keeper plays. It can be argued that the best defences limit good shooting opportunities, so perhaps it is inevitable that Joe Hart and de Gea would perform strongly here. In addition, a keeper will surely have a low error frequency if he is put under pressure less often by opposing attackers. As for passing accuracy, it is up to the defenders/midfielders to make a reasonable attempt to find a position to receive the ball. At the weekend, Newcastle’s goalkeeper Steve Harper made an unwise attempt to dribble past Danny Welbeck (did he not see my striker analysis which showed Welbeck to have the highest recovery rate last season?!) – as a Newcastle fan, I could not believe that the ball was passed back to Harper and neither full back: Ferguson nor Santon, dropped back to offer a wide short pass opportunity. A revisit to this analysis would require some thought to how to reduce the bias to the team in which the keeper plays.

This type of argument also applies to other positions where my analyses could be scrutinised and improved by further research on the key areas which contribute to the fields I used.

Fullbacks seem to need to have a combination of strong ground duel ability and an aptitude to join the attack as much as possible. Going forward they are heavily involved in linking play in wide positions but also must have excellent reactions and positioning to defend one-on-ones against attacking wingers without picking up yellow cards too frequently. Strong aerial duel prowess is not necessary but would obviously be a bonus, as would goals and assists.

Centrebacks need to be strong in both ground and aerial duels, and the more assured they are on the ball the better as ‘unsuccessful ball touch’ is introduced to the analysis. Central defenders with a high clearance rate are useful for teams expected to be in the lower reaches of the league, whilst high passing accuracy is more important for the top teams. A decent goal scoring record (from corners/set pieces) is again a bonus.

Defensive midfielders are regularly under pressure from opposing attackers and midfielders. Good tackle success, interception rates and recovery rates are important. Being able to retain the ball is also important so one touch lay-offs and passing accuracy are useful in this position whilst heading ability or a propensity to find a teammate in an advanced position can be considered a bonus.

Central midfielders are most important going forward than in defence. As a result goals and chance creation were biased by my review, alongside good passing success in the middle third and ground duel success. Low dispossession rates are also important.

Wingers/wide attackers need to have some ability in retaining the ball in the opposition’s half. The more often the player in this position finds space to receive the ball the better the chance of creativity so a good touch per min rate is also useful. Dribbling is a bonus skill – whilst of greater importance is chance creation / goals. Defensive attributes such as ground duels and recoveries are notable but in general secondary to attacking qualities.

Central attacking midfielders are all about chance creation, ball retention and goalscoring with no serious defensive qualities neccessary in open play (positioning may be another matter). The central attacking midfielder is likely to see more opportunities to play through balls or shoot than other midfielders, hence a good shooting ratio and opposition half pass success are most important.

Like central attacking midfielders, strikers who have high shooting accuracy and goal conversion rates along with chance creation are most valuable. Heading, dribbling and recovery rates are next important to players in this position.

My dream team (and squad) for last season based on the position review series is below. The players included obviously performed best overall in the areas discussed above. I have modelled the team for 3 of the more popular starting formations to ensure coverage for every position I reviewed in my series:

This compares to the PFA team of the season listed below:

Pos. Player Club
GK Joe Hart Manchester City
DF Kyle Walker Tottenham Hotspur
DF Vincent Kompany Manchester City
DF Fabricio Coloccini Newcastle United
DF Leighton Baines Everton
MF David Silva Manchester City
MF Yaya Touré Manchester City
MF Scott Parker Tottenham Hotspur
MF Gareth Bale Tottenham Hotspur
FW Robin van Persie Arsenal
FW Wayne Rooney Manchester United

Compared to the PFA team Coloccini, Baines and Bale are not in my form team of the year although the rest are at least in my ‘squad’, if not in the starting line-up.

I can also show an alternate England team based on English players’ rating in these positions. Of course some of the players were either not included, injured or retired from international duty over the summer but it provides a different perspective on the England team that could have gone to Euro 2012.

The last comment I will make is the incredible performance of Manchester City players in all reviews because in every position City were represented by a player in the top 2 except central attacking midfield – in which Agüero (who came 2nd in the striker review in any case) still finished in the top 5.

Comments welcome.

Premier League 2011-12: Position Analysis ST

Last, but by no means least, is my position review for strikers in last season’s premier league. Robin van Persie, rightfully acclaimed for his performances last season (in which he appeared in all 38 of Arsenal’s games, starting 37 of them – and even scored 2 from his solitary subsitute appearance against Stoke) bagged 30 goals in total. But he still didn’t quite manage to top this rating.

Before I discuss the results, I ought to discuss some formalities about the rating I have used.  As with most of my previous posts, I reviewed the statistics from players who started in the position of striker: that is, the central player in a 3-man forward line, both players in a ‘flat’ forward 2 or the lone player up front. By looking at player starting statistics only, I am perhaps unfairly judging players who made a habit of having an impact from the bench – in addition, as you will also see later, my goals scored below for RVP is ‘only’ 28 because of this filter.

I then shortlisted the strikers who played greater than 1000mins from the start (34 in total), and added Agüero to make a 35th because according to Opta he mostly played behind the central striker last season and so would not have otherwise qualified. Notable absentees from the list include Defoe, Balotelli and Jelavic – all of whom played over 800mins in games they started but still not enough to make the cut.

I looked at Opta key statistics and reviewed the correlations between these fields and Wins, Draws, Losses – purely for strikers. For the strongest correlating fields I calculated ratios to try and remove some bias towards playing time and team biases eg. the players who played for better teams generally had more shots on target so to dilute this bias I created a shooting accuracy ratio to judge shots on target vs shots off target.

The table of statistics above is ordered by playing time from Papiss Cissé (1037mins) to RVP (3311mins). It is dominated by shooting and goalscoring statistics, with additional credit for chance creation, passing accuracy, dribble success and recoveries. I toyed with the idea of including offside frequency, because it IS quite significant in its relation to wins but I still couldn’t bring myself to add it into my rating. It does however show which players are so keen to break through the last line of defence they fall foul of being offside very often: the top 3 ‘offenders’ were Hernandez, Best and Bent. The players least likely to stray offside were Rooney, Doyle and Torres.

Papiss Demba Cissé was the standout candidate for killer instinct, leading the way in goals per shots on target (0.63), 2nd behind Bent in general shooting accuracy and 4th for shooting accuracy inside the box.

Steve Morison, Yakubu and Rooney scored well in headed goals and accuracy, whilst the best creators of chances were van Persie, Suarez and Zamora.

The best dribble success ratios were held by Klasnic, Carroll and van Persie – whilst Helguson kept it simple all season with 0 dribbles attempted! (I gave him the average success ratio so as not to unfairly disadvantage him).

Terrier-like high recovery rates were found with Welbeck, Rooney and Ngog.

I weighted all of these factors based broadly on contribution to WDL in order to calculate the following final ranking:

*Offsides, on the far right, have not been counted in the total score.

Rooney just about steals the top spot ahead of Agüero, a good 7pts ahead of RVP in a re-jigging of the top goal-scoring charts for the year. Rooney’s statistics are basically a lesson in how to be an excellent all-rounder, and he would be almost 20pts ahead of the competition if it weren’t for the inclusion of the rather dubious ‘touches inside the box’ statistic which disadvantages deeper-lying forwards.

Surprises in the top 10 include Zamora, Holt, Klasnic and Best. Best in particular was probably 3rd or 4th choice striker at Newcastle last season but was never given the faith that his statistics seem to justify.

Andy Carroll and Fernando Torres, part of an £85m transfer merry-go-round in January 2010, are 23rd and 24th respectively and underperformed their collegues Suarez and Drogba.

The only positive in Louis Saha’s stats (35th, last in the list) was his decent passing accuracy. Niklas Bendtner, now at Juventus, who would surely be higher in my rating if I included an ego statistic, only finished 29th.