Why do teams win more often at home?

Teams win more at home because of a bundle of small edges that add up: a supportive crowd, familiar surroundings, no tiring trip, conditions the visitors aren't used to, and, surprisingly often, referees who lean slightly toward the home side without realising it. The effect is real. A 2006 study by The Times found that home teams in the English Premiership could expect to score about 37% more goals than visiting teams.

The referee part is the most striking. A Harvard researcher, Ryan Boyko, studied 5,000 Premier League matches and found that every extra 10,000 fans in the stands added about 0.1 goals to the home advantage. Home teams were also awarded more penalties, especially by inexperienced referees. A Sports Illustrated report went further and concluded that officials, unconsciously swayed by the crowd, were the main source of the advantage.

The pandemic ran an accidental experiment. When COVID-19 emptied arenas in the 2020–21 NHL season, home teams did 10% worse while road teams' win rates rose by 7%.

Some places have physical tricks too. Denver's thin, dry air lets baseballs fly about 10% farther, and Bolivia plays at 3,600 metres in La Paz, where it once beat Argentina 6–1. There may even be something primal at work: footballers' testosterone levels are significantly higher at home, echoing animals defending their territory. Other research suggests that no single factor explains it; it's the combination that tips the balance.