Many of you have heard the theory (advanced by author Tobias Moskovitz) that home court advantage can really be attributed to the behavior of referees favoring the home team, rather than players performing better on familiar turf. The theory works as such: Refs are unconsciously habituated by fans booing when they make a call against the home team, and cheering when they make a call against the away team. As a result, referees end up calling a greater number of fouls against the visitors, and a lesser number of fouls against the home squad. As we have already seen in an earlier post, more foul calls for a team = a higher number of points for that team, thus accounting (or so the theory goes) for a historically proven higher winning percentage for teams playing at their home location. In this analysis, I wanted to see if refs actually did, in fact, call a significantly higher number of fouls against away teams. If this ended up being the case, I also wanted to see the effect of this discrepancy on point totals.
Results: I found that for the 2014-2015 season, referees called a disproportionately high number of fouls against away teams (20.63) when compared with fouls that were called against home teams (19.96). This difference in means of .67 fouls per game was found to be significant at the .000 level (std. deviation of .74), and of the 63 referees that I included in my analysis, 52 called more fouls against away teams than against home teams. The most biased referees in this regard were Derek Richardson and Dedrick Taylor, with an Away Fouls – Home Fouls differential of over 2.5, which is more than 2 standard deviations above the mean.
The next thing I wanted to see was if this discrepancy in fouls called between home and away teams contributed to a corresponding points discrepancy. More specifically, I would expect that refs who called a higher number of relative fouls against the away team, would also see a higher point differential (in favor of the home team) in games they worked. I actually found that this was not the case, as referee’s Home-Away Score Differential was not significantly correlated with their Home-Away Fouls Differential (Pearson correlation of .02, significant at the .886 level). Although home teams scored on average 2.42 more points per game (std. deviation of 1.44, significant at the .000 level) than away teams, it seems that foul differential alone was not enough to account for this difference.
Analysis: As predicted, refs during the 2014-2015 NBA season called more fouls in favor of the home team. And although home teams did indeed score more points than away teams during this season, the fouls differential alone was not enough to account for this difference. These results seems to suggest that there is more to the concept of “home court advantage” than simply referee bias, whether this be the home players’ familiarity with the environment, the home players having fans cheering for them, or a multitude of other factors. In the future, it would be interesting to see if team’s statistics other than foul shots attempted are significantly better when they play at home. It might also be of value to consider looking at whether larger home crowd numbers contribute to a larger home court advantage, although this has already been examined to some extent.