Monday, 12 December 2011

Chelsea Shouldn't Chase Clean Sheets.

Ever since Chelsea's Performance Director mentioned in an interview that "there is a stronger correlation between clean sheets and where you finish than goals scored and where you finish.",there's been a spate of blog posts extolling the virtues of clean sheets.To be fair to the guy he didn't explicitly say that Chelsea were actively using strategies designed to increase their number of clean sheets,but there was certainly an implication that more clean sheets were always a good thing to aspire to.

At first glance the evidence seems compelling.If you keep a clean sheet,you're obviously not going to lose.Score and it's three points and on average you'll pick up upwards of 2.5 points from matches where your opponents remain scoreless.However,by looking at how many points a team gets when they successfully keep their goal intact you are omitting those games where a team goes out with this defensive strategy and it fails.The question a Performance Director should be asking is are the points we get when the strategy works sufficient to compensate for the occasions when we concede a goal (or two) and find ourselves with insufficient time or offensive resources to make an adequate response.You've got to account for the games where you adopt a passive approach,but succumb to a late goal and are unable to reply with a goal or two of your own.

In short,is an overtly defensive strategy the best way for every team ?

If your going to go for clean sheets your games are likely to have less goals,so let's see how a team such as Chelsea fare in first an environment where less goals are scored.Chelsea typically score 70% of the goals scored in their games,so in a low scoring,clean sheet orientated environment where say 2 goals a game on average are scored,they will score 1.4 goals per game and allow 0.6 goals.If we now simulate season after season using these parameters we find that Chelsea,if they adopt a clean sheet strategy will gain on average of 1.97 points per game.If we now simulate seasons where Chelsea still score on average 70% of the goals scored in a game,but this time they adopt a less defensively minded approach and their games now on average see 3 goals per game scored.In an environment where goals,both scored and allowed are more likely and clean sheets are less common a much superior team will see their points per game jump to 2.15.

An average of 2 total goals per game is abnormally low,but it has been chosen to emphasis the effect of a changing goal environment.However,the trend for a superior team to do better in a more goal laden situation is consistent.Over more typical ranges an attacking approach will yield a team of Chelsea's quality around 3 points a season more than if they opt to try to prevent their opponents from scoring.

Chelsea have the wealth and prestige to attract the best attacking talent available,therefore they would be better served forgetting about trying to increase their quota of clean sheets and instead take a more attacking approach and challenge their opponents to keep up.It'll get them more points in the long run and they should leave overtly defensive strategies to teams with less attacking resources.

Footnote.Headline from Daily Mail following Chelsea conceding a late equaliser in a 1-1 draw at Wigan."Chelsea paid the price for negative play, admits AVB after dropping points at Wigan."

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  1. AVB seems to agree as well.....

  2. Cheers for that link anon....Chelsea manager agrees with "The Power of Goals"....I like it :-)