How much do crowds affect winning in the NBA?

The Los Angeles Clippers and the Los Angeles Lakers are an interesting case study in the effect of home court/field advantage. Not only do they share the same city, but the same stadium. And they play each other a few times a season.

The court and decorations are changed to reflect who is officially the “home” team for those games. And, more importantly, the stands are full of the home team’s season ticket holders.

Everything else is roughly the same. Both teams have likely slept in their own beds, have family close by, are in familiar routines and places (training centre etc.), and haven’t just stepped off a plane.

This is a good natural experiment on the effect of crowds. Economists put the Staples crowd to the test five years ago and found:

…crowd effects are sizable in motivating a home team win, raising the likelihood of such an event by between an estimated 21 and 22.8 percentage points. The point estimate implies that essentially the entire home advantage between the two teams is attributable to the crowd effect.

You can really see it in the following chart, with a couple dozen more games being played since.

Data scraped from Basketball Reference.