by Dashiell Nusbaum
Alternate link to story: https://medium.com/push-the-pace/the-factors-that-influence-nba-home-court-advantage-2a5a602f8c1f
Many see sports as the ultimate “equal playing field” — where the same rules, regulations, and opportunities exist for all, where the best team will emerge victorious. This isn’t always the case.
We find the existence of a “home court advantage” across sports, where teams are more likely to win at home than away. This is especially true of the NBA, which has the largest home team advantage among the four major American sports. The existence and magnitude of a home court advantage has been extensively studied; however, we lack an understanding of the factors that cause certain teams to have larger home court advantage than others.
I found the average regular-season home court advantage for all 30 NBA teams from 2008-09 through 2018-19. Home court advantage is a team’s winning percentage at home minus their winning percentage on the road. For example, from the 08-09 through 18-19 season, the Denver Nuggets won 75.62% of their home games and 46.52% of their away games. Therefore, Denver’s home court advantage = 75.62% – 46.52% = 29.10%.
My data begins in the 2008-09 season, as this was the first season following the NBA’s last major relocation, when the Seattle Supersonics relocated halfway across the country to become the Oklahoma City Thunder. Since then, only one other team, the New Jersey Nets, has changed states. The Nets migrated a mere half-marathon away to Brooklyn, with no significant change in home court advantage after the move.
Home Court Advantage By Team
Home Court Advantage By Team (2013 Arena Locations)
I believed the following factors might have an impact on home advantage:
- Overall Winning Percentage
- Home Attendance Percentage (percent of seats filled at home arena)
- Fan Loyalty/Quality (explained below)
- Distance From Other NBA teams (using 2013 arena locations)
- Altitude of Arena
- Population of Metropolitan Area
- Home Referee Bias (16-17 and 17-18 NBA 2-minute report)
The above stats are all fairly self-explanatory except for fan loyalty. I calculated the loyalty rating by plotting attendance percentage vs. winning percentage, and calculating how much higher or lower a team’s attendance was than would be expected given the team’s winning percentage.
Teams that performed poorly but had large home attendance numbers received a better fan loyalty/fan quality rating than teams that had attendance numbers much lower than expected for their team success.
Winning percentage, altitude, fan loyalty/quality, and metropolitan population were significantly correlated with a home advantage in my model. The four factors appear in that order from left to right, with their associated distributions, in the plots below.
Interestingly, fan loyalty and metropolitan population were negatively associated with a home court advantage. I initially believed that a higher population would harm away teams, who might stay up late partying in exciting cities far from their homes. In addition, I assumed “better” fans would motivate teams to play better at home.
These unexpected results may be related to the ongoing discussion in the NBA about rest. Previous studies have found that days of rest impact winning percentage. Given that the NBA has trended toward increasing rest on road trips via scheduling fewer back-to-backs at the league level and practicing less on the road at the team level, it is possible that visiting teams may have made gains in rest that counteract the effects of the night life in larger cities.
I also did not anticipate finding an inversely proportional relationship between fan quality and home court advantage. Perhaps more passionate fans and a more exciting environment create a chaotic climate for players, which in turn harms their performance.
I then created a model which predicts home court advantage based on these four factors. The model explains 57.37% of teams’ home court advantage.
As previously noted, factors associated with rest and relaxation seem to be important. This lines up with the current popular discourse about the roles sleep and rest play in athletic performance. With this in mind, it is not exactly shocking that Denver, Indiana, Portland, Utah, San Antonio, Charlotte, and Memphis top the list of teams with the best home court advantage. Future research could explore the arenas themselves (noise, lights, etc.) or the alleviation of altitude advantage to help mitigate certain road disadvantages.
Home court advantage is not necessarily a bad thing — arenas are mainly populated with home fans, who want to see their team win. Home advantage means more people get to see the result they want. This only becomes a problem when different home teams have different advantages, or in the playoffs, when certain teams get to play more games at home.
Denver’s advantage is more than twice that of Brooklyn, due to factors unrelated to on-court performance. To achieve a truly equal playing field, especially come playoff time, the league may want to look into changing that.