Tuesday, 2 July 2013

Do Goalkeepers Raise Their Game Against Big Clubs

Goalkeepers are traditionally very hard to analyse. There are understandably less statistics produced due to goalkeepers generally having less actions during a game, although the modern day goalkeeper needs to have added excellent distribution to his repertoire to effectively play as a sweeper. The limitations of the available statistics is probably for another post but the obvious one is whether a shot should be expected to be saved. Paul on his Different Game blog has already explored some excellent work on goalkeepers

Joe Hart was in unbelievable form during Manchester City's title winning season

From a throwaway line I heard on Match of the Day some time ago, I decided to investigate the impact playing against better teams had on keepers. In essence are performances like John Ruddy away at Liverpool for Norwich in securing a point reflective of their performance over the season or are they “one offs”.

Using the MCFC analytics data, which is now unfortunately a season out of date (here’s hoping they continue to release updates on a better than annual basis although the project does seem to have died a death) we have access to a full seasons worth of data using statistics provided by Opta. By working out how many shots each team face on average we can see whether the % they save is higher or lower against the ‘big 6’ (in this case I have used Man Utd, Man City, Chelsea, Arsenal, Spurs & Liverpool – sorry Everton fans!!)

In all 44 Goalkeepers played during the 2011/12 season for the 20 Premier League Teams and the first thing I looked at was how shots & goals affected the final league position.

It’s clear from the graph below there is a reasonable correlation between the number of shots faced and where teams finished (R Square is 0.6484). It’s common sense that the more shots teams have at you EVENTUALLY one is likely to go in, so conceding less shots initially should result in conceding less goals. Using Shots Conceded is effectively half of the Total Shots Ratio Model in reverse as with that model the percentage which you outshoot your opponent has a high relationship with finishing position – it means that if you concede less shots you are much more likely to be able to outshoot your opponent and ultimately finish higher.

Graph showing total shots faced vs final league position for 2011/12

The second graphic shows the number of goals actually conceded and is an even better fit, with an R Square of 0.7027. There are some outliers here (Sunderland conceded as many goals as Arsenal but there were 10 places between them – it’s OK not conceding many but you do actually have to shoot and score sometimes!)

Graph showing total goals conceded vs final league position for 2011/12

So knowing this I go back to my original point and whether some goalkeepers are able to raise their game against the big boys.

I chose a cut off of 1350 minutes (15 games) to look at, which gave me 22 goalkeepers. The gap between Thomas Sorenson (1350 minutes played) and the next 3 keepers in total minutes (3 at 720 minutes) was reasonably large anyway and a good place to cut.

First to look at is the total number of shots on target (excluding penalties) each goalkeeper faced. We can see from the simple table below which keepers immediately stand out.

Minutes per shot on Target

Minutes per Goal Conceded

Minutes per Goal conceded vs Minutes per Shot Faced

Immediately Joe Hart stands out as much better than the rest (remember, this is 2011/12 data so his dip in form last season is not taken into account) whereas at the other end Adam Bogdan and Jussi Jääskeläinen are both in the bottom 4 keepers in terms of the lowest number of minutes per goal conceded. This goes some way to explaining why Bolton were relegated.

So where it was taking just 2.5 shots on target to beat Paul Robinson it was taking twice this many to score past David de Gea. Not bad for a keeper who supposedly had a poor first season!

David de Gea is now proving to be the top class Goalkeeper he was signed to be

I’ve now compared the figures against the previously mentioned big 6 against the other teams. For this I have removed Sorenson, Jaaskelainen, Begovic and Bogdan due to them not playing enough games against the better teams. I set a minimum of playing at least 2/3rds of each of the games against the big 6 and the other 13 to give a reasonable representation.

Minutes per shot faced - Big 6 vs Other 13

In all cases the big 6 shot on target more frequently than the other 13. This was pretty much to be expected as you would expect the better teams to produce goal scoring opportunities more frequently than lesser teams.

Shots per goal conceded - Bg 6 vs Other 13

This is where it gets interesting, there is no clear distinction showing keepers raising their game against better teams. Michel Vorm, Simon Mignolet and Mark Schwarzer all have excellent records against the big 6 and along with Paddy Kenny all actually conceded less goals per minute against the better teams than the others in the league.

Joe Hart is also in there, and although his record is good in both cases it’s better against the better teams, maybe a lack of concentration in the less important games due to being so well protected?

David de Gea and Brad Friedel come off worst, de Gea’s phenomenal numbers against the other 13 teams (Man Utd always seem to have an exceptional record against teams lower down the table) was always likely to drop against the better teams, but it remains as one of the better ones in the league. Brad Friedel shows a big drop and maybe the 5-1 home hammering Tottenham took by Man City (remember Dzeko’s 4 goals??) from only 9 shots on target skews the data and shows the fragility of how one result can affect this.

Unfortunately these statistics only show the tip of the iceberg. Is there a reason for keepers performing better against better teams? They are likely to have more defenders in the box making the shooting opportunity not as clear, maybe they take shots from further out. All this is speculation and until further detailed information is available speculation is all we have.

Another goal flying in past Paul Robinson

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