Defense really is half the game

Every so often, some ornery old basketball hand will remind us all that "defense is half the game," and that when we concentrate mainly on the offensive end of the game, we're ignoring a critical component of team success.

While it sounds reasonable, it isn't necessarily true. Yes, defense is "half the game" in the crudest sense. Inevitably, the average team will spend half its time on defense. But this doesn't mean that defense plays the same role as offense in determining team victories: maybe most teams are close to the average on defense, and offense is where the variance that produces "good" and "bad" teams actually occurs.

In fact, when you think about it, this is a testable hypothesis. Why not just measure the standard deviations of offensive and defensive efficiency in the NBA, and see which turns out to be more important? John Hollinger conveniently provides us with these numbers on his team statistics page. 

What's the answer? It turns out that defense really is half the game. In fact, at least in this year's sample, it's a little more than half the game, with a standard deviation of 3.39 compared to 3.18 on the offensive side. 

Maybe the New York Times was on to something...