Prompted by a tweet from @RandyHauser, I decided to have a look at some keeper stats and whether keepers had a weak side.
I would like to see stats on goalies. When the punch crosses, when they catch. Are there goalies teams cross less often on? Do they have a weakness on one side or another? Stuff like that.
— RandyHauser (@RandyHauser) November 28, 2017
Below is a plot for Premier League, Bundesliga, and La Liga keepers for 2012/13 to 2016/17 who’ve faced more than 50 shots on target in a season, along with the difference between their save percentages for SoTs to the left side and right side of the goal*.
(To just focus on the size of the differences, all values are positive, rather than one side having a negative value and the other positive)
The average difference between directional save percentages is 7-8%, but clearly the more shots on target faced the lesser chance of a big difference.
This ‘one season problem’ – where keepers probably don’t face enough shots for the stats to weed out noise – has appeared when people have tried to look at how keepers perform versus Expected Goals, but I will leave it to more expert minds to judge to what extent it seems to be a problem here.
** mid-writing update**
Realised that smushing together the seasons on record would yield larger samples. Here is the plot, for the keepers used in the previous one.
The average difference in direction here is just 6%, but you can see the continuing trend towards 0 with more shots added. Even so, even for players who’ve faced more than 200 shots on target, it’s not unusual at all for a difference of up to 10 percentage points to remain.
I won’t come to any conclusions here about the data, and will leave it to more expert minds to do so.
*left and right is literally split down the middle for the point at which the shot is recorded as having ended, whether that is through save or crossing the line. Any values which were directly in the middle were put into the ‘right hand side’ box, as most keepers are likely to be right-handed and therefore favour making saves to their right. I’m aware that this isn’t perfect.