The Importance of Position on Offense and Defense

Perimeter players aren’t as important on defense as bigs. And bigs aren’t as important on offense as perimeter players. I’ve heard this assertion made quite a few times. I’ve even made it myself. But is it true? When I wrote the post arguing that Trey Burke should be an early lottery pick rather than a mid-first-round pick , I noted that Burke’s “troubles” on defense are not particularly concerning because he is a point guard, not a big. This got me to thinking: sure, certain bigs have way more impact on defense than any perimeter player could ever hope to, but does that mean bigs are more “important” on defense? Instead, isn’t the difference between a good big on defense and a bad big on defense the same as the difference between a good guard and a bad guard? The best defensive guards have much less of an impact than the best defensive bigs, but aren’t the worst defensive guards as substantially worse than the worst defensive bigs? On the other hand, isn’t the discrepancy between Garnett and Bargnani (or Larry Sanders and David Lee, if you’re a Goldsberry fan) a lot bigger than the discrepancy between say, Rajon Rondo and Steve Nash? Then again, maybe it isn’t.  I decided to investigate.

In order to answer my questions, I looked at J.E.’s 12 year RAPM data, which includes every player’s regularized APM from 2001 to 2012. I excluded players who played less than 20,000 possessions because their RAPM values are much more uncertain. I separated all players by position with an assist from basketball-reference. Then I looked at the offensive and defensive ranges for each position.

I found the following:

On defense,

• ~95% of point guards fall between -4.1 and 2.3 per 100 possessions (a range of 6.4)
• ~95% of shooting guards fall between -3.6 and 2.3 (a range of 6.0)
• ~95% of small forwards fall between -3.5 and 3.3 (a range of 6.8)
• ~95% of power forwards fall between -3.5 and 4.2 (a range of 7.7)
• ~95% of centers fall between -2.4 and 5.7 (a range of 8.1)
• While there is a bit of a difference across positions – i.e., centers may be a bit more important than guards – the difference is not statistically significant (e.g., the hypothesis that each position will have the same range is accepted). This is true even if we include the entire range for each position and not just two standard deviations from the mean.

On offense,

• ~95% of point guards fall between -3.4 and 4.2 per 100 possessions (a range of 7.5)
• ~95% of shooting guards fall between -3.8 and 4.3 (a range of 8.1)
• ~95% of small forwards fall between -3.8 and 3.8 (a range of 7.6)
• ~95% of power forwards fall between -4.2 and 2.7 (a range of 6.9)
• ~95% of centers fall between -5.2 and 2.6 (a range of 7.8)
• Again, the variance on offense among positions is not statistically significant.

Here are a couple of graphs for those who like visualizing data:

So, basically, as we expected, the big guys are better on average on defense and worse on average on offense. But when we look at their ranges, their relative importance is pretty much the same. Now, of course, more work needs to be done here. 12 year RAPM is likely a good overall indicator, but it’s certainly not the ultimate source for everything (nothing is). It would be interesting to see a study like this replicated using other data, whatever it may be. But, for now at least, it doesn’t appear that certain positions are significantly more “important” than others on either side of the ball, though they can certainly be more impactful. Starting a little guy at center, for example, is obviously a bad idea. But the difference between a bad center and a good center doesn’t seem to be significantly different from the difference between a bad guard and a good guard.

-James