In yesterdays preview of Stoke (link) I threw in a plot showing how they compared to teams that have been relegated from the Premiership which I figure is worth some elaborating on.
To quickly recap, a teams total shots ratio is calculated as follows:
Total shots ratio (TSR) = Total shots for/(Total shots for + Total shots against)
The higher a teams TSR the more they control the ball. The importance of TSR lies in it’s predictive ability – being the best stat I have for predicting a teams future performance (link).
The crux of the plot is reproduced in the plot below: the relationship between points and total shots ratio.
The correlation is pretty strong here but that’s not necessarily the point. The take-away message is that teams that control the ball will gain better results and thus more points.
Lets go ahead and colour that plot in a bit. So below black represents the title winners, blue represents the teams that qualified for the champions league and red represents teams that were relegated.
There’s a pretty clear pattern here – those teams that control less of the ball (i.e., those to the left of the plot) are far more likely to be relegated whereas it’s very hard to win the league, or qualify for the champions league, without controlling a majority of the ball. The only real outlier is the blue spot to the left of the plot – being Everton’s qualification in ’04-05.
Finally we can break this plot down and determine the probability of qualifying for the champions league/being relegated based on a teams TSR. To eliminate some of the noise the data is plotted as a three point moving average.
There’s not a lot of overlap there – it paints a pretty clear picture that controlling the ball is an integral part of being a successful team.