Tuesday, 20 March 2012

Evaluating EPL Defenders.

The attributes of attacking players in whichever sport are usually easier to quantify than those of defenders.Individual stats such as shots,shots on target are readily available and are strongly correlated to goals scored,which in turn correlate with team success. Therefore,there is a credible chain running from onfield actions of strikers through to the eventual success of his team and this allows us to begin to attach numerical estimations to that strikers contribution.

In the case of defenders the correlations are much less clear cut.We can reasonably suggest that a successful tackle or interception made by a defender is a good thing for his side,but these positive actions don't accumulate positive results,such as goals.Instead they prevent unwanted occurrences such as goals conceded.And it's plain that counting up goals scored (in the case of strikers) is much easier and more accurate than counting goals prevented (in the case of defenders).Quantifying something that has happened is always preferable to quantifying something that hasn't.

If we want to be able to evaluate defenders in a similar way to strikers,we need to be able to correlate their on field actions to events that contribute intrinsically to the final result.And an obvious way to do this is to see which defenders are "best" at doing things that correlate well with how often a team concedes a goal.We are beginning to have access to much more extensive player data especially in the EPL and statistics such as tackles lost,ground duels lost and aerial duels are just three of the likely candidates that could correlate to goals allowed by a defence as a whole.

Of the three,ground duels lost by defenders has the strongest correlation to goals allowed by a team and the relationship is in the expected direction.The shorter the time between defenders losing out during a ground duel,then the more goals their team can expect to concede on average.To take an example of extremes,Hull's defenders were beaten during ground duels once every 22 minutes,that's about 17 times a game for a back four and they allowed almost 1.7 goals a game.While by contrast Liverpool's defenders were beaten once every half hour or 12 times a game and allowed just 0.7 goals per game.

These numbers are of course a broad brush description of a Saturday afternoon.Not all duels lost by defenders will be lost in a defensive context,although the majority will be and not all defensive ground duels will be lost by defenders.Hopefully though there is enough integrity in the numbers for the conclusions that losing ground duels is bad for a team to be valid and therefore a defender who can minimize the amount of such contests he loses is a prized asset.However,before we can move to a player by player analysis we need to process the player statistics.

 Playing time will impact on the amount of duels a defender loses(if you're not on the pitch,you can't be beaten in a one on one),so I've allowed for actual playing time,including substitutions when calculating how often a defender is beaten.Secondly,I've allowed for the quality of the team in which a player is performing.I'd imagine it's easier being a defender for ManU than it is being on for Bolton where the amount of attacks you are likely to have to defend will be greater.If a defender is losing three ground duels a game in a team who are as a whole losing 20,then the probability is that he may be a better defender than someone who is also losing three duels,but in a side who concede only 10 such "defeats" a game.Thirdly,hindsight is a powerful tool,so I've listed the best defenders of ground duels from each EPL side from the 2008/09 season and shown where they are now.This should allow us to decide if the view of their defensive abilities based on this statistic in 2008/09 were vindicated by future events.

The overall defensive rating for ground duels comprises two ratios.the Total Ground Duels Ratio is derived from how often a defensive player is engaged in a ground duel compared to the average for him and all other defenders from his side.A figure in excess of 1 indicates that the player is engaged in more often in such contests than is usual for defenders from his side.This indicates how often a player is involved in crucial in game events compared to his team's norm.

The second part of the rating is the Ground Duels Lost ratio.This is simply the time between ground duel defeats for the player divided by the average time for him and his team mates.So again a figure in excess of 1 indicates that the player is of above average efficiency at avoiding defeat in ground duels compared to his team mates.

These are the 20 best defenders,one from each team from the 2008/09 EPL season.Ideally you would like your player to be involved in above average numbers of challenges and be of above average efficiency during those challenges.Fulham's Hangeland stands out on that basis,but unsurprising names such as Vidic,Cahill,Distin,Givet and Turner would appear to be exceptional contestants in one on one contests.

Best Defenders at Dealing with Ground Duels for each EPL Team 2008/09.

Player. Team in 2008/09. Total Ground
Duels Ratio.
Ground Duels
Lost Ratio
Current Situation.
G. Clichy. Arsenal. 1.31 0.82 Sold to ManC for £7 million.
M Laursen. A Villa. 1.55 0.80 Retired due to injury.Villa "legend."
G Givet. Blackburn. 0.67 2.57 Blackburn regular.
G Cahill. Bolton. 0.91 1.41 Sold to Chelsea for £7 million.
B Ivanovic. Chelsea. 0.96 1.29 Chelsea regular.
J Yobo. Everton. 1.06 1.18 On loan at Fenerbahce.
B Hangeland. Fulham. 1.19 1.17 Fulham regular.
M Turner. Hull. 0.83 1.46 Sold to Sunderland for £6 million.
J Carragher. Liverpool. 0.81 1.55 Still a Liverpool player.
N Onuoha. ManC. 0.78 1.40 Loaned to S'land.Sold to QPR for £3 million.
N Vidic. ManU. 0.99 1.42 Man U captain.
D Wheater. Middlesbro' 0.95 1.25 Signed for Bolton in 2011 window.
S Bassong. Newcastle. 1.14 1.15 Sold to Spurs for £8 million.On loan at Wolves.
S Distin. Portsmouth. 0.79 1.83 Sold to Everton for £5 million.
A Faye. Stoke. 1.08 1.08 Stoke player of year,now at WHU.
P Chimbonda. Sunderland. 0.98 1.10 In Championship for Doncaster via Blackburn and QPR.
M Dawson. Spurs. 1.24 0.94 Still at Spurs.
L Barnett. WBA. 0.93 1.43 Playing for Norwich in EPL.
M Upson. WHU. 0.85 1.37 Stoke squad player.
M Figueroa. Wigan. 1.02 1.05 Wigan regular.

The majority of the players are still playing at the highest level of competition and where they have dropped in class,age or injury are possible secondary factors.Four of the five defenders who were transferred for big money were rated well above the average of their team mates in terms of avoiding defeat during ground contested duels,although not necessarily in terms of the number of ground duels contested.This could indicate that good one on one strength is valued in the EPL along with the ability to organise others to do some of your work for you.

It's also worth noting that some of the worst defences can contain some of the best defenders and this could explain why defenders are generally worth much less than strikers.A subject touched upon here.An outstanding forward will probably produce goals because his team can chose to provide him with the majority of the chances.By contrast an outstanding defender may simply be forced to watch as his less talented defensive colleagues are picked on by the opposition.Buying a forward may guarantee goals,but buying a defender may mean you need to buy one or two others before the expected improvement materializes and it opens up the possibility of investigating if four average defenders produce better defence than two outstanding ones and two below average ones.Is a defence as good as it's weakest link?

The majority of the players listed have proved to be above average defenders over the ensuing two and a half seasons,indicating the likely value of these kind of statistics,so in  a future post I'll post up this season's ground duel leading defenders.

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