The Slow Death of Home-Field Advantage
The benefit of playing at home has never been smaller. What happened?
The N.F.L. season kicks off tonight, with the Kansas City Chiefs hosting the Houston Texans. Due to social distancing, the Chiefs will permit about 16,000 fans at Arrowhead Stadium, which is about 22% of the stadium’s capacity. The limited seating has led some to wonder how much home-field advantage there will be in 2020, as 26 of the league’s 32 clubs will not be permitting fans in the first week.
But what if home-field advantage pre-Covid-19 was overrated to begin with?
Last year, home teams in the N.F.L. won just 52% of their regular season games, the worst win rate since 1972 and the third lowest in the Super Bowl era. For comparison, home teams in the early 1990s won 60% of their games.
If you account for the point spread, it gets worse. Last season, home teams covered (winning by a larger margin than the point spread) in just 43.7% of games, the worst rate since at least 1966.
Home field being overvalued isn’t a recent phenomenon, either. In five of the last six years (and 13 of the past 16 years), home teams in the N.F.L. covered the spread in fewer than half the games.
Historically, betting handicappers have awarded home teams a three point advantage for hosting the game. For teams with particularly loud venues, like Seattle or New Orleans, the advantage may be a tick higher. Conversely, for teams that struggle to sell out the stadium, a smaller advantage is given.
A statistical analysis demonstrated that between 2005 and 2018, home field advantage in the N.F.L. was worth about 2.4 points per game. That same model now projects that home field advantage in 2020 will be worth less than half a point.
Las Vegas handicappers have taken note. “If I had a home-field advantage worth 2.0 points (on a projection), I am using 1.5 this season,” ESPN sports betting analyst Preston Johnson said. “On top of that, we have four months of international data in baseball and soccer (without fans this summer) that shows home-field advantage is not that much. Fans just don’t matter that much.”
But why? Why, as one researcher notes, is the “home-field edge slowly declining over the years?”
One factor we can exclude is noise. Stadiums have gotten larger and louder over the decades. The world record for loudest crowd roar was set a few years ago in Kansas City at 142.2 decibels. Advances in certain fields, like private air travel, sports psychology, and sports nutrition have also negated some of the obstacles of playing on the road.
The real answer as to why home teams still have a small but waning advantage is most likely refereeing. In 1999, the N.F.L. approved instant replay and coach challenges to check perceived referee mistakes. The following year, the home win rate fell from 60% to 56%.
It is important to remember that referees are people, after all. As such, there is an innate desire to not be booed or ridiculed by penalizing the home team in a crucial moment. Studies have demonstrated that in soccer, for example, referee home team bias is reduced when the crowd is smaller or if there is a track around the pitch, further adding space between the referees and a potentially hostile crowd.
The home team bias among referring has been measured in other sports besides football and soccer, too. “In baseball, during a full count, more pitches are called strikes for the home team’s pitcher,” says Konstantinos Pelechrinis, an associate professor of Computing and Information at the University of Pittsburgh.
“In the N.H.L., referees call 20% fewer penalties for home teams, which is equivalent to about 0.25 goals. (In the N.B.A.) the home team is awarded on average approximately 0.8 more free throws, or 0.6 points per game,” he added.
Mostly because of refereeing, there is still an advantage. It’s just not as big as you think.