I was reminded of this last weekend when my son's team (which I coach) was consistently called for offside by one of the linesmen (which the ref duly followed), while the other linesman did not. But I digress. Back to punishment: what are the patterns? One way to see if there are trends or cross-league differences is to look at trends in the Big Four leagues of soccer. One easy way to see if there are patterns and to quantify their size is to look at yellow cards - a common enough occurrence in a match to yield some interesting and sufficient data. So here are trends in yellow cards since the 2005-06 season per team/match.
Overall, teams see about two yellows per match played. But clearly, refs in some leagues more easily pull out the card than in others. In particular, refs in La Liga give significantly more yellows than refs in the Premier League. La Liga's 2.5 yellows per team/match easily dwarf the Premiership's roughly 1.5 cards. Whether this reflects differences in playing style, instructions from the league, training of refs, or more skillful diving in Spain's top league is unclear, but punishment is clearly not meted out equally. We see consistently more yellows over the years in Spain and Italy than in England and Germany (perhaps suggesting something about the diving argument). (There also are a couple of interesting trends, with the Bundesliga refs decreasing their enthusiasm for yellow somewhat over time.)
Given these different baselines across leagues, another way to think about inequality in punishment is to see if some teams are systematically more likely to receive yellows than others. Here, the obvious explanation may be home field advantage. As avid readers of this blog know, the home field advantage in offensive and defensive production is a fairly consistent pattern across leagues and over time, but with some clear exceptions for particular teams, as I tried to point out in an earlier post. But does this extend to another kind of home field advantage: namely, an advantage in penalties assessed?
Well, let's look at the data. The story here is very straightforward:
away teams "earn" systematically more yellows than home teams. The size of the difference is about .25 in the Bundesliga and Serie A, and closer to .5 in the Premier League and La Liga. Thus, the home team advantage in penalties - that is, inequalities in punishment - are most pronounced in the EPL and La Liga Primera. But whether this is due to biased refs or something else more objective - like more fouls and different kinds of fouls committed by home and away teams - is a question for another post.
