"Football Freakonomics": How Advantageous Is Home-Field Advantage? And Why?

The following is a cross-post from NFL.com, where we’ve recently launched a Football Freakonomics Project.

Do home teams really have an advantage?
Absolutely. In their book Scorecasting, Toby Moskowitz and Jon Wertheim helpfully compile the percentage of home games won by teams in all the major sports. Some data sets go back further than others (MLB figures are since 1903; NFL figures are “only” from 1966, and MLS since 2002), but they are all large enough to be conclusive:

So it’s hard to argue against the home-field advantage. In fact my Freakonomics co-author Steve Levitt once wrote an academic paper about the wisdom of betting (shh!) on home underdogs (more here).
But why does that advantage exist? There are a lot of theories to consider, including:

• “Sleeping in your own bed” and “eating home cooking”
• Better familiarity with the home field/court
• Crowd support

Those all make sense, don’t they? In Scorecasting, Moskowitz and Wertheim compile data to test a variety of popular theories. You might be surprised (and maybe even disappointed) to read their conclusion:

When athletes are at home, they don’t seem to hit or pitch better in baseball … or pass better in football. The crowd doesn’t appear to be helping the home team or harming the visitors. We checked “the vicissitudes of travel” off the list. And although scheduling bias against the road team explains some of the home-field advantage, particularly in college sports, it’s irrelevant in many sports.

So if these popular explanations don’t have much explanatory power for home-field advantage, what does?
In a word: the refs. Moskowitz and Wertheim found that home teams essentially get slightly preferential treatment from the officials, whether it’s a called third strike in baseball or, in soccer, a foul that results in a penalty kick. (It’s worth noting that a soccer referee has more latitude to influence a game’s outcome than officials in other sports, which helps explain why the home-field advantage is greater in soccer, around the world, than in any other pro sport.)
Moskowitz and Wertheim also make clear, however, an important nuance: official bias is quite likely involuntary.
What does this mean? It means that officials don’t consciously decide to give the home team an advantage — but rather, being social creatures (and human beings) like the rest of us, they assimilate the emotion of the home crowd and, once in a while, make a call that makes a whole lot of close-by, noisy people very happy.
One of the most compelling (and cleverest) arguments in favor of this theory comes from a research paper by Thomas Dohmen about home-field advantage in Germany’s Bundesliga, the country’s top soccer league.
Dohmen found that home-field advantage was smaller in stadiums that happened to have a running track surrounding the soccer pitch, and larger in stadiums without a track.
Why?
Apparently, when the crowd sits closer to the field, the officials are more susceptible to getting caught up in the home-crowd emotion. Or, as Dohmen puts it:

The social atmosphere in the stadium leads referees into favoritism although being impartial is optimal for them to maximize their re-appointment probability.

So it looks like crowd support does matter – but not in the way you might have thought. Keep this in mind next time you’re shouting your brains out at a football game. Just make sure you know who you’re supposed to be shouting at.