Tobias Moskowitz and Jon Wertheim address this question in the fascinating article “What’s Really Behind Home Field Advantage?” that appeared in the January 17 issue of Sports Illustrated. (This article is taken from the new book Scorecasting: The Hidden Influences Behind How Sports Are Played and Games are Won by the same authors.)
Appropriate data is collected to address some of the “myths” about home field advantage. Many people believe home teams win since their crowds boost players’ performance, but the authors give evidence that the crowd doesn’t have an influence on home team performance. Other “myths” are that home teams win because the rigors of travel hurt the visitors and the home teams benefit from a kinder, gentle, schedule. But there is no evidence from data that these beliefs are true. Another popular belief that is refuted is that home teams benefit from unique characteristics of the home playing field.
Okay, so what is really behind home field advantage? The authors claim that there is a general referee bias to favor the home team in sports. This claim is supported by several studies. In baseball, the umpire will decide if a pitched ball is a strike (inside the strike zone) or a ball (outside of the strike zone). Home team hitters are less likely to have a pitched ball called strike than the visiting team hitters. Likewise, home team players generally have an advantage in stealing a base, and scoring from second base on a single base hit. Also, interestingly, the home team bias is larger when the particular play is more important in deciding the outcome of the game.
This referee bias carries over to other sports. In soccer, in close games when the home team was ahead, the referees had a tendency of reducing the length of the allotted extra time to make up for lost time (the so-called stoppage time). In American football, the away team is more likely to receive penalties and the size of the bias increases in more crucial situations that impact the game outcome.
Are the referees deliberately favoring the home team? The authors think not. They believe that the umpires are (like all of us) susceptible to social pressure, which in this case is the home crowd, and this social pressure causes the bias.
This is interesting stuff and I’m interested in doing my own data exploration to learn more about the home advantage in sports. But certainly this study has implications on how referees are trained or chosen in sports.