I asked the nice people at Infostrada Sports Group for a whole slew of data with regards to penalties taken in the Premiership and they were kind enough to provide me with it. They can be found online and on twitter.
I think we all know that home teams have an advantage during a Premiership match, a long time ago I looked at just how big this was during a game for a whole host of parameters (link) but does this also translate to penalties?
The answer is yes. Home teams receive a significantly larger fraction of the penalties awarded than their visiting opposition, ~65% more in fact. That gap seems particularly large to me, especially given that home teams only take ~30% more shots.
The other neat bit about this table is the pretty large difference in the conversion rate between home and away teams. When we’re looking at sample sizes up around 400 penalties there’s a significant chance that this is due to something other than luck. Maybe this whole table can be summed up by pressure, the home crowd pressuring referees to award penalties and, when a decision does go against them, causing the opposing player to miss their penalty.
Another alternative may be that players are more likely to miss a penalty given a particular score, for example when the game is close as opposed to a game you are winning or losing by a large number of goals. Does this translate to reality?
Well there is a noticeable dip in conversion rate towards the centre of that plot – lending credence to the idea that crowd pressure could be a possible explanation. It’s also worth highlighting that when the home team is a goal behind they are 160% more likely to win a penalty than the opposition. I’d suggest that this also adds credence to the ‘crowd pressure’ scenario.
The downside to this plot is that there are significant sample size issues at play here, with 83% of all penalties being taken when the score is either tied or a team leads by a single goal. Thus the next plot is similar to that above but this time the data is grouped by game state in order to provide some more statistically significant results, with the number above each bar shows the number of penalties being represented.
This gives a bit of clearer picture I think. In each scenario the away team receives less penalties than their hosts and compound this by converting a smaller proportion of them.
To summarise this post: no matter how I cut the data home teams win more penalties and convert them more often.
Next time I finally hit the stuff I find really interesting. Which teams win/give away the most penalties? Is there any correlation to possession? Are better teams better at taking penalties? How about saving them?