How much is a clean sheet worth?
In September last year Soccer By The Numbers tested a suggestion from Mike Forde, Chelsea’s Performance Director, that there is a “stronger correlation between clean sheets and where you finish than goals scored and where you finish.”
The post found a clean sheet to be worth roughly the same as three goals; that is if you fail to concede you can expect the same amount of points on average as if you score three goals in a match. It’s a startling statistic, giving credence to the idea that good teams are built ‘from the back’.
I thought I’d expand this across two seasons worth of data (2009/10 and 2010/11) and compare the ‘big four’ leagues. The chart below illustrates the comparison for goals conceded; a team that keeps a clean sheet can expect, on average, between 2.6 and 2.7 points per game across these leagues.
Clean sheets are worth the least in Italy, no great surprise given the Serie A produced more 0-0s (65) than any other of the three leagues over the two seasons. Overall, the trends match those found in the aforementioned Soccer By the Numbers article, with the most stark difference in expected points between one and two goals conceded.
There is no great variation between the leagues, though it appears conceding two goals in the German Bundesliga isn’t as catastrophic as in other major European leagues, with teams collecting 0.77 points on average compared to around 0.6 in England, Spain and Germany.
The big interest is a comparison with goals scored; three goals (2.7-2.8 points) are worth only marginally more than a clean sheet in the last two seasons.
Again, a clean sheet is perhaps worth even more than most realise. Of course the data merely accounts for the ‘average’ team – the best teams will find that clean sheets are even more valuable given their propensity to score.
In the context of the current Premier League season, the numbers look good for Swansea, who have been particularly stingy with goals conceded at home. Often compared to Blackpool, the Swans have already kept as many clean sheets as the 2010 play-off winners, whose consistent defensive failures ultimately cost them their place in the top flight. A lack of goals should not concern Brendan Rodgers yet.
Equally, Manchester United have discovered (domestically at least) the value of keeping it tight at the back following their humbling defeat to Manchester City at home.
So, across Europe it appears swashbuckling attacking intent is perhaps a weaker strategy than a conservative defensive approach, if such a trade-off exists. Unfortunately, it’s not always the best way to please fans.