Home court advantage in basketball

We all feel the Celtic ouch and perhaps some of us delight in it.  Matt writes:

Kevin Drum notes two smart responses to the question of why home court advantage is so big, with one hypothesis pointing to the refs and another pointing to the idea that there are actually lots of differences from arena-to-arena.

Of course if the arena is the difference you would expect shooting guards, who need a good feel for the lights and angles of the basket, to have a bigger relative advantage at home than do the dunking big men.  That should be easy enough to test.  And maybe a look at Lakers-Clippers or Nets-Knicks history can clear up the importance of arena by holding geographic area constant. 

I wonder if a third component of home court advantage has to do with sleep.  People sleep better at home, if only because they don’t have to go to such great lengths to get sex.  I recall reading that Larry Bird became a truly great player only once he…um…calmed down a bit.


In a sport where effort can make such a big difference (just how hard are they running to get to their defensive or offensive positions?) the emotion and encouragement of the crowd might also have an effect.

Vanderbilt's Memorial Gym is an interesting case for this. As far as I know, it's the only major basketball arena currently in use that puts the coaching benches at the ends of the court rather than the sides. It's a clever way to give the team a home court advantage: they split their season 50/50 at Memorial and on normal courts, but visiting teams are only exposed to the weird arrangement about once a year.

The difference is due to evolution - home players have a higher level of testosterone. This has been measured in soccer matches in England. Players spit into cups just before the match.

From an evolutionary game theory perspective, this is a stable strategy of being a hawk at home and a dove away - leads to fewer confrontations and genetic collusion to progress the species... (or something like that if I remember right)

another reason why homecourt advantage is important:


"Word is, Boston entertainment prince Patrick Lyons might have played a role in the Celtics' blowout Game 7 win over the Hawks a week ago that vaulted them to the second round. The Hawks stayed at the Liberty Hotel May 3 in Cambridge before playing the Celtics. A league source said Lyons, who operates the Alibi Lounge in the hotel, instructed his bar staff to give anyone affiliated with the Hawks a double shot in any alcoholic beverage they ordered."

I (and others in the field of sabermetrics) have argued that HFA is higher in basketball becaust he game is "longer". There are about 100 possessions for each side, and points are scored frequently. This is long enough for one team's talent advantage to come out much more frequently than in basball, where their is much more variance of outcomes and the game is "shorter".

Put another way, if basketball games were only half as long, the HFA would be much smaller. If thy were twice as long, HFA would be larger.

HFA is a function of the variance of outcomes per "atom" of game play, and the number of "atoms" in a game.

I would argue that there's nothing special about home court advantage in basketball vs. other sports, except in terms of the "length" of the game.

My own argument for this is on page 3 here.

Not sure how isolating out Clippers/Lakers games goes when they play in the same arena, though (both play their home games at the Staples Center).

Phil: Baseball is a completely different beast. In baseball the road team is at a huge disadvantage as
it has to bat first.

I heard there was a baseball player who had five young children at home and when he was on the road his batting average went up about 100 points.

It's now deep into playoff season in the NBA, which means that opponents are much closer to each other in true ability and talent. Other factors outside of team talent, such as home court advantage, would mean the difference in games more often, and therefore appear to be especially strong. The effect of the home court is the same, but the teams are so closely matched that other factors begin to dominate--home court

Also, Phil is absolutely right about HCA being based on the number of iterations. The NBA game is 8 minutes longer than college basketball, and it has a quicker shot clock. This leads to many more possessions per team. Each possession can be thought of as just a mini-game, in which HCA has a small effect. The greater the number of possessions, the greater the cumulative effect of the advantage. This is based on research specific to basketball, not baseball.

1. Testosterone levels and effort on defense. This one seems strong.
2. Foul shots and referees: See, e.g. the Utah Jazz, who are highly dependent on free throws and not fouling, and have huge home/road splits. Referees are affected, they are only human. Also seems strong.
3. Crowd noise and effort: see #3, but slightly different. This seems like it should affect bench players more.
4. Length of game and variance: I have a problem with that theory, which is football. Home-field advantage is incredibly strong in football, but games only have about as many possessions total as a baseball game has outs per side. Clearly you're right that it matters, but still we observe a much stronger home field advantage over time in basketball and football than we do in baseball. Going into a game between two even teams I believe WPA (win probability added) starts with the home team at a .55 chance to win.

That link is pretty clear that the effect is strong. HFA is generally considered worth 3 points in football.

One of the economics profs who taught me at university spends a lot of time studying sport, including statistically determining the existence or absence of referee bias. The evidence is pretty overwhelming that referees are biased in favour of the home team, because they're influenced by the crowd. One study showed referees identical gameplay situations and asked them whether a foul was committed. Some saw it with the sound off, some with the sound on. Referees tended to award fouls more often when they could hear the crowd, even when it wasn't there in the room. Another study found that referees in the German Bundesliga were signficantly less biased than those in the Premier League; this was because German football stadiums tend to have running tracks between the stands and the pitch, which means that the crowd is further away from the ref.

Of course, basketball courts are smaller and have fewer spectators than football stadiums, but the effect must surely exist even if it's smaller.

Here's a link to an article summarizing the testosterone theory of home advantage:


The lakers beat the Utah Jazz in game five of their series while shooting 14 more free throws than the Jazz. Of course, the game was in Los Angeles.

Want to bet that the Jazz will shoot at least ten more free throws in game six when the game is in Salt Lake City.

The NBA is about two steps away from being as scripted as Professional Wrestling. Different rules for all stars versus role players. Different rules at home games than away games. Different rules in the first quarter than the fourth quarters. And the last, manipulation that certain cities get the best draft picks.

Has anyone studied free throw percentage home-road splits? Does the fans waving those styrofoam sticks while the opposition is at the free throw line have an effect?

I have a hard time believing that a swing of several points is mostly due to a change of lifestyle and sleeping patterns on the road, or in the differences of the arena. The players are the best in the world, and they've honed their skills to such a degree that their performance shouldn't differ too much based on what they did earlier in the day or their surroundings. The courts are all the same dimensions and the basket is always 10 feet off the floor. If the lighting is significantly different, there's nothing to suggest that would favor players on the home team or that such bothersome conditions would be something they could readily acclimate themselves too. I don't quite understand the reasoning there.

Also, staying up late the night before hardly matters in the NBA, as most games aren't until the next night. In baseball, there used to be a ton of day games, and there are still a good deal more day games than in the NBA.

I believe refereeing does have a lot to do with it, and I wouldn't be all that surprised if the NBA encourages that type of home cooking as an unwritten rule. If the home fans are happy most of the time when they go to see their team, then they'll probably be more supportive of the team, and be able to forgive all those road losses. It makes the mediocre teams seem better than they are.

I don't see how a referee's judgment is significantly altered by which side he thinks will approve of his call. Possibly subconsciously to a small extent, but this is their livelihood, and what they've practiced at for years and years. They get into a pattern, and it doesn't make sense that that pattern would be interrupted to any noticeable degree because they're in a different city on Sunday than they were on Thursday.

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