The effect of the coronavirus outbreak has rapidly become one of the hot topics in sports, even bumping speculation about Tom Brady’s impending free agency from the front page of websites and newspapers.

Professional sports leagues have progressed in less than a week from saying that they were monitoring the situation to acknowledging the possibility that games might have to be played in empty arenas and stadiums, something that’s already started to happen in other countries.

The idea of playing in front of empty seats raises the question of how great the home-field advantage is under normal circumstances and what goes into that advantage.

The coronavirus break comes at a hectic time of year

Early March kicks off an exciting time of year in the sports world. Although the NFL season has concluded and the NCAA Tournament in basketball dominates the month, the start of spring training announces that the Major League Baseball season is on its way.

April means the arrival of The Masters as the NBA and NHL are heading to the home stretch of their regular season and setting the stage for the playoffs. On top of that, spring also brings one-off events like the Kentucky Derby and the Indianapolis 500 in May.

Besides being exciting, those events have something else in common: All are big spectator events and that raises the possibility that they may have to be conducted without fans as health experts try to contain the spread of coronavirus.

Data confirms that playing at home is an advantage

We don’t really need to crunch the numbers to know that playing at home is an advantage. It’s why pro teams battle through the regular season in order to get the extra home contest in best-of-seven playoff series.

Darren Rovell, the former sports business analyst for ESPN and CNBC now working at The Action Network, which focuses on the sports betting industry, pulled five years of numbers together showing the value of the home field varies by sport.

Home teams win 68% of the time in college basketball and 62.7% in college football to lead all major sports. However, the advantage is overstated because schools in the major conferences pack their non-league schedules with “buy games” – contests against inferior opponents willing to play on the road in exchange for more money than they could make by playing at home.

In the four major pro sports, the data shows homes teams winning at a 59.7% clip in the NHL, 58.3 in the NBA, 56.4 in the NFL, and 53.4 in Major League Baseball. Since those sports play schedules in which the quality of competition at home and on the road is closely balanced, the percentages confirm playing at home is an advantage.

What factors create the home-field advantage?

If betting lines and point spreads didn’t exist, making money by wagering on games would be an easy way to make a living since the home teams in the major sports win roughly four out every seven contests.

Rovell refers to the betting lines as “the great equalizer. In fact, college and pro football teams playing at home lose more often than they win if you account for the point spread. That begs the question: What factors contribute to the home-field advantage and how valuable are those components individually?

Playing at home usually means not flying in from another city the night before or early on the day of the game, which constitutes the first advantage. There’s also something to be said for sleeping in your own bed, eating meals at home, and just generally being more familiar with the arena.

The 18,000 fans attending a game don’t make free throws in basketball or score goals in hockey, but do they influence what takes place in front of them?

Harvard fellow Oliver Roeder reviewed 13,658 calls by basketball referees and found that visiting teams were more likely to end up on the wrong end of incorrect calls. That implies the possibility that the behavior of fans influences the officials. We may soon have meaningful data about how much of the home-field advantage comes from a good night’s best and how much comes from being cheered on by the local fans.