By Emma Young
When the US National Basketball Association (NBA) was forced to pause the season due to Covid-19 on March 11 last year, the fans were naturally devastated. When the season resumed five months later, with the top 22 teams bubbled together and playing every game in Orlando, Florida, this was great news for the sport, and the fans — and a pair of US researchers. Andrew McHill at Oregon Health and Science University and Evan Chinoy at Leidos Inc, in San Diego, realised that the restart provided a perfect natural experiment to explore the effects of travel on play. Their study, published in Scientific Reports, reveals some insights into causes of the well-documented sporting home-side advantage.
The “home-court” advantage, as it’s known in basketball, is apparent in the results tables: teams win more often at home than away. In normal circumstances, it’s hard, though, to disentangle all the possible variables that might underlie it. These include home-crowd noise, the discomfort of air travel, and time zone changes. In regular seasons, NBA teams do regularly travel long distances across the US, through one, two or even three time zones, to play away games. Many NBA players report resulting sleep loss and fatigue, and harmful effects on their performance, recovery and mood, the researchers note. Disruption to circadian rhythms has been considered the mostly likely culprit, though the rigours of travel and sleeping away from home have also been highlighted as potentially play a role.
To explore just how travel affects play, the researchers looked at the results of the 22 teams’ games before the pause, compared with their results while none were travelling and all were playing in one location, in Orlando. The pair also considered various aspects of the teams’ performances in each game.
In the first portion of the season, teams won 63.8% of their home games, and 50.8 % of their away games. McHill and Chinoy found, though, that there was only a disadvantage to playing away when a team had to travel across time zones, and not when they played away within the same time zone (the detrimental effects of travelling across time zones mostly occurred when teams travelled westwards, rather than eastward). When the teams were later all playing in Florida, with no travel (and only virtual fans), though a “home” and “away” team was designated for each game, there was no “home” advantage.
The researchers then looked more closely at various aspects of play. They found that when teams travelled across time zones, their shooting accuracy suffered. They also lost more possessions and scored fewer points per 100 possessions (indicating that they were playing more defensively). But even when a team played away and didn’t cross time zones, they played a more defensive game, and they got a lower percentage of the offensive rebounds (an event that gives the offensive team another opportunity to score).
McHill and Chinoy also found that when the teams did not travel, while bubbled, the typical home-court advantages for shooting accuracy and rebounding were reduced. “Thus, home-court advantage in professional basketball appears to be linked with the away team’s impaired shooting accuracy and rebounding,” the pair writes. They add that these “may be separately influenced by either circadian disruption or the general effect of travel, as these differences manifest differently when teams travel within or across multiple time zones.”
Athletes in other major sports, including baseball, also travel regularly across time zones. If basketball shooting accuracy is taken as a measure of movement precision, and this is worsened by such travel, this could help to explain the home-side advantage — or the away-side disadvantage — in these sports, too. As the researchers also note: “Future work is needed to explore other athletic events where travel schedules can impact performance to further elucidate travel and circadian factors.”