What Is Total Shots Ratio? And How Can It Improve Your Understanding of Soccer? (Mike L. Goodman, August 12, 2013, Grantland)
As with lots of analytics concepts, TSR is just a fancy set of letters for an incredibly simple idea: Let’s count shots. Specifically, TSR is the ratio of how many shots a team takes versus the number of total shots (actual equation: shots for/(shots for + shots against). For example, Manchester United took 562 shots and conceded 494 shots last season. That works out to a TSR of 0.53. And it turns out counting shots is pretty important. Because goals are so rare, and can be scored in such odd and wonderful ways, a team’s past scoring record isn’t a particularly reliable predictor of future goals. Looking at how frequently a team shoots predicts future goals much more accurately. In that way, it’s similar to baseball’s run differential. If you want to predict how often a baseball team will win, figure out how much better they are at doing the thing that leads to winning (scoring runs). If you want to figure out how often a soccer team will score goals, figure out how often they do the thing that leads to scoring goals (shooting). TSR is a measure of a team’s ability to take shots while preventing opponents from shooting.
Why Bother With TSR?
The biggest thing that TSR has going for it is that it works. A team’s point tally is definitely correlated with how good its TSR is (for some actual math on how highly correlated TSR and points are, you can check out Martin Eastwood’s work on the subject).
The biggest problem with soccer as played in its major leagues is not the imbalance in finances, but the style of play that follows from their spending. When a big budget team plays a small budget team the latter will play defensively and try to absorb shots in hopes of scoring a fluke goal on one of their minimal attacking opportunities. In essence, they stack TSR against themselves. They play to lose.