About Home Teams Winning

May, 14, 2008
5/14/08
4:31
PM ET

TrueHoop reader Kurt e-mails:

I was a little frustrated with the home team dominance of the second round of the playoffs (home teams are 17-1). So I started to look around for people to blame for this phenomenon. Naturally, I landed on the NBA refs. So far in the second round, the home teams have shot an average of approximately 4.6 more free throws a game. Home teams have attempted 500 and Away teams have only attempted 416. Obviously 18 games is not the best sample size (I ran a t-test and the p-value is .15 which isn't great), but an 86 free throw discrepancy feels significant.

The home teams are shooting a much better percentage and thus they are actually making about 4.6 more free throws a game as well. That is a 4.6 point head start for home teams. With teams so evenly matched this year is their any question that the referees are playing a big role in the strength of home court advantage?

This is a chicken-and-egg thing. Surely, at home, you feel more confident, and thus drive harder and more often to the hole. And then you get more fouls called on you.

Also, for whatever reason, the team that is more aggressive in general seems to get more leeway from the referees. There's a 20,000 word essay in there somewhere.

So, what I'm saying is, referees are indisputably part of homecourt advantage. But how much of that is referee bias is very tough to say.

Now, whatever portion of those 4.6 points per game is attributable to bias, or a human desire to please those 20,000 screaming people, or whatever it is -- is it deciding games? Maybe, here or there. Which is really not great. But it's probably not a big trend.

Justin Kubatko of Basketball-Reference tells me that the average margin of victory in this year's playoffs so far is 13.3 points per game, which is much more than the 11.5 average margin in the regular season. 13.3 would also be the biggest such margin in history, if it holds up. (It was 13.1 in 1959, 12.9 in 1964, and 12.8 in 1996. Remember Little House on the Prairie? They had that general store where you could buy anything from an egg to a sheet of glass. Justin is like that with basketball statistics. And I should add he's feeling pretty confident about his position in the Stat Geek Smackdown right now.)

UPDATE: TrueHoop reader Daniel:

Home teams are 17-1. A team that is behind at the end of a game is likely to foul to try to extend the game. The away teams have fouled at the end of the game, giving the home team free throws. The reader that you quote says that the home team has shot 500 free throws, while the away team has shot 416, but how much of that is just in the last 5 minutes of the game? I bet that 1st, 2nd, and 3rd quarter free throws are much closer. This isn't to say that refs or comfort at home leading to aggressiveness is a factor, though not to the degree that was suggested by the reader. 

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