Re-examining Homecourt Advantage

“I came out of Bataan and I shall return”-Douglas MacArthur on arriving in Australia in 1942

One of the interesting side effects of changing jobs is losing my laptop. I turned it in on Friday and since then I’ve felt like I’m missing an arm. I’ve been working on my wife’s laptop (which is a less than ideal scenario for all involved) and it’s kinda sucked. Yesterday’s piece took about four times as long as normal, while I adapted to my new writing/number crunching scenario reality. But I adapted and I persevered.

Let’s get back to work.

You Big Baby

Probability of Home team winning a game (Win %)

= (Projected Wins Home Team-Projected Wins Road Team)/82 +.606

=Win %: (Proj. Home Team Win% – Proj. Road Team Win%) +HCA(.606)

You’ve seen this before on this blog (Go here for the Basics). This is the simple equation I came up with for the home team winning  a single game (see here for detail). I’ve used this  for the evaluation of our predictions among other things (see here) and it does a pretty good job.

But you know by now that pretty good just doesn’t cut it.

We're all about excellence

When I first worked out Homecourt advantage I simply went looking for available data. The data set was the percentage from regular season games  from 1999 thru 2008 (in which the home team wins 60.6% of time) and as I said before this was good and worked fairly well. A number of my readers have made many suggestions. Here’s the list of things that I’m going to do here:

  • Add in the effect of rest days and back to backs.
  • Add in the effect of altitude
  • Use a more recent data set.

The first thing to do is build the data set. For that I turned to our old friend over at  dougstats .

Dude, thanks for the info

I downloaded every game for the last five years (and before you ask see here ). And I went about adding the rest days and altitude. I did that as follows:

  • For rest days, I chose three levels:
    • 0 for back to backs
    • 1 for day of rest between games
    • 2 for >2 days of rest
  • For Altitude, I also chose three levels:
    • Zero to low elevation (430′ or below): Boston, LA, Memphis, Miami, New Orleans, Sacramento,New York City,Orlando,Dallas,New Jersey,Toronto,Houston,Seattle(gone but not forgotten),Portland,Golden State and Washington (hi Ted!)
    • Some elevation (430′-1117′): Charlotte (Jordan with just some elevation seems wrong somehow), Milwaukee, Chicago, Cleveland, Atlanta, Indiana, Detroit, San Antonio, Phoenix, Minnesota
    • Nosebleed Country (5300-9400′): Denver and Utah

Now, If I simply work out the percentages here I won’t account for the strength of the opponent. Luckily, we already know the formula for two opponents on a neutral court:

Probability of  Team A beating Team B at a neutral site = (Raw Win Production Team A (Sum of ADJP48*MP/48 for all players on team) -Raw Win Production Team B (Sum of ADJP48*MP/48 for all players on team))/82 +.500

So if I use the total raw win numbers for each team for the season to calculate the win probability for each game if it was played at a neutral site, I can average it out (through the magic of large sample sizes) and figure the homecourt advantage in each scenario over playing at a neutral site. That  table looks like so:

If I add in .500:

Some interesting findings. Both, altitude and rest days affect the Homecourt advantage and they interact with one another. Average HCA is at 59.9%.  Altitude is directly proportional to HCA . Rest days are a little stranger.  Altitude directly interacts with rest. Denver and Utah kill teams at home if they have a rest edge but they get killed themselves if the other team is coming in with at least a two day rest edge.

Tomorrow, I give you power rankings.


  1. 11/8/2010


    on thrusday, the lakers will go to denver. both teams by then will of had two days of rest. does this suggest denver will enter the contest with a home winning percentage of 60? i want the lakers to go undefeated as long as possible >:o

  2. Eliot

    Nice work! The rest day factor for the high altitude games is really interesting, I had no idea it had such a big effect on team performance.

  3. Dan

    It looks like your sample size is too small, at least for the high altitude teams. It doesn’t make sense for there to be such a huge difference between games where the road team had 1 day of rest and games where they had 2+ days of rest, with the direction of that difference flipping depending on how much rest the home team had. Getting 2+ days of rest rather than only 1 gives the road team a 26% advantage if the home team has 0 rest (61.8-35.7), but it gives them a 24% disadvantage if the home team has 2+ rest (53.3-77.8).

    • Fred Bush

      If you’re tired, you can’t handle the altitude. If your opponent is less tired, you’re hosed.

  4. Spider Jerusalem



  5. 11/9/2010

    So high-altitude teams should probably slow down the tempo when they have no rest and are facing a well-rested team. And they might even be able to increase their already large advantage by playing at a faster tempo in all the other situations…or just be happy with the advantage they have and leave pace unchanged.

  6. 11/9/2010

    Oh, and I don’t see OKC in the list of cities – did you include OKC games?

    Switching computers is a bitch, isn’t it? I’ve been dealing with using multiple computers for months now.

  7. Ben R.

    I had a thought about another possible tweak–what about teams going on extended road-trips? If a team is gone for 5 or 6 games, especially if they’re traveling long distances, I wonder if their play deteriorates a little in the last couple games (or, on a smaller note even, if a single road game a few thousand miles away has a larger effect than a road game nearby)? Though, sometimes I feel like teams win the first few on a road trip and carry some momentum going into the last couple (then again, I’m aware that concepts like “momentum” often don’t really exist, and are just a mirage of random luck being more clumpy than you’d normally think–so maybe that part is just me being stupid).

    I love the piece (and your work in general!), and if someone already mentioned this then my bad. I was just curious if that might be another possible upgrade to the homecourt advantage analysis.

    • Ben R.

      Also, I know what I mentioned would probably be a tremendous pain in the ass…

  8. […] differential for his team. Now there are some additional factors to consider. Where you play your homegames is important (i.e. the Jazz and Nuggets players are teeing off from the kiddie tee and I’ll probably […]

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