NBA Home Court Advantage
by Trevor Whenham - 01/11/2008
Two days after the lowly Charlotte Bobcats went into Boston and handily beat the Celtics probably isn't the best time to talk about the home court advantage in the NBA, but let's do it anyway. The perception among many sports bettors is that the NBA has a particularly strong home court advantage. Statistically, the numbers show that they aren't entirely wrong. The home teams won 60.4 percent of the games played in 2005-2006, and 59.1 percent last season. Twenty eight of the 30 teams in the league last year had a better record at home than on the road, and Boston had the same bad record home and away. Only Detroit won more roads games, and in that case they were very solid on both fronts - 26 home wins and 27 on the road. Eighteen teams won at least seven more games at home than on the road. In other words, there really is no disputing that playing at home in the NBA gives teams a significant edge.
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The real trick is figuring out, in real terms, just how significant the home court advantage is. It's one thing to say that the home team has an advantage, and that is clear, but if you are unable to quantify the advantage then it is very difficult to meaningfully compare two teams to see who has the edge. This is obviously especially a problem if you are playing the point spread. In that case it's not good enough to know who is going to win. You need to know how much they are going to win by. You could quantify the home court advantage if you were really determined to, but it's easier to use what others use to quantify the edge. Sonny Moore, the complier of power rankings for more than 30 years, sets the home court advantage at three points. That is to say that if two perfectly matched teams were to play, the team that is playing at home would win by three points. If the same teams were to play on a neutral court they would theoretically play to a tie. Jeff Sagarin, the well-known statistician from USA Today, adjusts his home court advantage throughout the season to reflect what is going on at that time. As I write this he currently has the home court advantage set at 2.56 points.
That's the theoretical way to handle the point spread, but bookmakers don't always handle it that way. There may be a perception out there that those who set the odds add three points for the home court advantage, but a look at real games shows that that isn't precisely true. The best way to look at the impact of the home court advantage is to look at cases where teams play a home-and-home series. The difference between the two spreads tells us how bookmakers view the different locale, because we can assume that the matchups and other factors that go into setting a line won't have changed significantly in the day or two between games. For example, when Phoenix played at the Clippers on Dec. 27, they were favored by 8.5 points. The next night the two teams played in Phoenix, and the Suns were favored by 13.5. That means that, assuming other factors remained approximately equal, the Suns were viewed to be five points better in Phoenix than they were in L.A. The impact was even more extreme for the Lakers. They were favored by three when they hosted the Warriors on Dec. 9. They covered that game fairly easily, yet five days later they traveled to San Francisco for a rematch and they were six point underdogs. This situation varied slightly because both teams played in between, but neither team had a huge edge in rest. What we can see, then, is that the home court advantage can vary widely in real terms depending upon the perception of the oddsmakers and the public.
What this shows us above all is that you can get yourself into real trouble with your handicapping if you take the lazy route and assume that home court advantage will have the same basic impact in all cases. There is a clear example of that this year in the NBA. Portland (22-13) and Orlando (23-14) have the same basic record. Given that, a lazy assumption would be that they would have approximately the same home court advantage. If you don't think to hard about it, that makes sense - they have about the same number of wins over about the same number of games, so you could guess that they have done about as well as each other at home. If you made that mistake, though, it could cost you a fortune. Portland is a stellar 17-3 at home, and a much less impressive 5-10 on the road. Orlando, on the other hand, has a very unexpected record. They are a concerning 7-8 at home, and a stunning 16-6 on the road. The home court advantage the Blazers enjoy is extremely different that the 'advantage' of the Magic.
The lesson from this? As with everything else in handicapping, there is no short cut to success. You can look at three points as a guideline for the impact of the home court advantage, but that's only a starting point. From there you have to look at how the teams involve perform at home and away, what form the teams have been in lately, and everything else that can affect the outcome of a game. In other words, the home court advantage is a factor in NBA handicapping, but not one that should affect your decisions more than other factors. If a team has a big matchup advantage it is likely to win regardless of where the game is played.