How Homecourt Advantage Will Impact the NBA This Upcoming Season — The Playgrounder
Anybody who follows the Chicago Bulls (or has watched The Last Dance) knows what happens to the United Center when the song “Sirius” by the Alan Parsons Project is played. The lights dim as you hear the first few notes and watch animated bulls run through Chicago on the Jumbotron. The electrons in the air pulse with electricity, the building rocks on its foundations, and the PA blares: “Aaaaaaaaand now, the starting lineup for your Chicago Bulls!” At the height of the Bulls’ run, it felt like they were unbeatable at home.
It’s a similar story at many NBA arenas. The NBA has the strongest homecourt advantage of the major American professional sports, with home teams winning 58 percent of games in the past 10 seasons, by an average of 2.7 points per game. This means that the average NBA team has been 5.4 points better at home than on the road over that timespan. Vegas odds have reflected this, with home teams generally favored by about the same margin on the spread. In recent years, homecourt advantage has slightly decreased; last season, even before the bubble, teams were only 4.3 points better at home than on the road, and home teams won 55 percent of games.
This advantage will likely decrease even further this season as many teams will not allow any fans, while the teams that do will allow only limited fans. Obviously, it is unsafe to have fans in arenas while a deadly contagious disease runs rampant, but it will be sad to watch games without the atmosphere of a packed NBA arena.
In the past, NBA teams have played particularly better at home and worse on the road when in front of big crowds. This is consistent with other sports as well, and there are a variety of possible reasons as to why, including referees succumbing to human nature and getting influenced by home crowds. Regardless of the reason, any impact of crowds on homecourt advantage is likely to be severely muted this season.
But fans are not the only reason for the NBA’s historic strong homecourt advantage; after all, other leagues play in front of loud crowds as well. In the NBA, there is also a schedule-related reason; road teams generally play on less rest than home teams. Notably, a road team is nearly twice as likely to be playing the second game of a back-to-back as a home team.
Schedule Breakdown, 2009–10 through 2019–20
1 day of rest
14 percent of games
This really hurts road teams; as you might expect, teams play better the more rested they are, with the effect plateauing after 4 days of rest.
The impact of rest is even more pronounced when looking at the rest difference between opponents; teams at a rest disadvantage to their opponents win less frequently than those with no difference or a rest advantage. Because of the NBA’s schedule, road teams have long been at a rest advantage far more than home teams have been.
But this is something that will change this season. This year, the NBA has reduced the amount of back-to-backs and introduced baseball-like series where teams play two games in a row against the same team, at the same location. This could help eliminate some of the rest disparity (since these opponents will have the same amount of rest for at least the second game of the series), and reduce travel. Both of these factors will likely reduce homecourt advantage this season.
Announced 2020–21 Schedule through March
1 day of rest
20 percent of games
Interestingly, teams have won more as they get deeper into road trips. Road teams win 41 percent of the time on the first four games of road trips, but 44 percent on games after the fourth game. This could be a product of small sample size-nearly 95 percent of road trips are four games or fewer-but it makes some sense. Time zone changes and cross-country flights cause teams to be fatigued, but by the fifth game of a road trip, teams have often adjusted to their opponents’ time zones.
This could be important in this upcoming season, as teams will be going on longer road trips than usual. From the 2009–10 to 2019–20 seasons, 45 percent of road trips only lasted one game, the average road trip was a mere 2.1 games, and only 5 percent of road trips lasted five games or longer. In the upcoming NBA season, just 21 percent of road trips will last one game, the average road trip will be 2.6 games, and 12 percent of road trips will last five games or longer (more than double previous seasons).
Another factor in homecourt advantage is travel. In the data in past seasons, this shows up most clearly when teams cross time zones, but only in a specific circumstance. When eastern teams travel west, where the games are played later, they win under 40 percent of the time. Western teams traveling east, or teams playing in the same time zone as their home city, do not suffer as negative of an effect.
This helps explain why Western Conference teams own 7 of the 10 largest homecourt advantages. When they do play Eastern Conference teams, those teams have struggled to play on the west coast. Another possible factor is altitude; the Denver Nuggets have the strongest homecourt advantage, and the Utah Jazz rank sixth.
At the other end of the spectrum, the Brooklyn Nets, Chicago Bulls, and Milwaukee Bucks have had weak homecourt advantages. These are all Eastern Conference teams, who do not benefit from the time zone effects shown earlier.
Nightlife has commonly been cited ( sometimes cheekily) as a reason for teams to struggle on the road. The argument is that players might party too hard the night before a game when they go to a happening city. This does not really show up in the data; the Los Angeles teams are both towards the bottom of the top ten in homecourt advantage, but Miami, Houston, and the Knicks are middle-of-the-pack, and the Hawks and Nets are at the bottom (though they were in New Jersey for some of this time).
In other leagues that have resumed play at home stadiums without fans, home field advantage has lessened. Data scientist Luke Benz has a Github page with detailed results from various soccer leagues around the world. He found that while most leagues have seen some reduction in homefield advantage, most leagues do still have some degree of home-field advantage present. The English Premier League, in fact, has seen no noticeable drop in homefield advantage at all despite not having fans in the stands for games. Meanwhile, Ben Baldwin, an NFL writer for The Athletic, found that homefield advantage in the NFL has almost completely disappeared this season.
The NBA is likely to have a less-pronounced homecourt advantage this season, and not just due to a lack of fans in the stands. Schedule changes will make it so that road teams face less rest disadvantages than they did before, and teams on longer road trips will have more opportunities to get used to time zones on the road. Still, there will likely be some level of homecourt advantage, since there will still be travel to road games. Even in the bubble, when nobody was even traveling, there was still some degree of homecourt advantage (“home” teams won 52 percent of the time, by an average of 1.3 points per game). This will be a weird season, with a December start, limited fans, and the Raptors playing home games in Tampa (which could decrease their homecourt advantage even further). A weaker-than-usual homecourt advantage will make it all the weirder.
Originally published at https://www.theplaygrounder.com on December 16, 2021.