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I'm sure this has been answered before but a google search turned up nothing.

Basketball-reference defines DEF-RTG as:

"Defensive Rating (available since the 1977-78 season in the NBA); for players and teams it is points allowed per 100 posessions." (Yes they spell possessions wrong but that's not the point)

Hollinger on ESPN.com defines DEF EFF as:

"Defensive Efficiency - the number of points a team allows per 100 possessions."

I think most would agree that these definitions are essentially identical.

So why are the numbers completely different? For example, the '08 Celtics have a 98.9 DEF-RTG but a 82.2 DEF-EFF.

I assume that they each have different definitions for what constitutes a possession? B-R provides a definition while Hollinger does not.

Sixerscan wrote:So why are the numbers completely different? For example, the '08 Celtics have a 98.9 DEF-RTG but a 82.2 DEF-EFF.

I assume that they each have different definitions for what constitutes a possession? B-R provides a definition while Hollinger does not.

The ESPN numbers are wrong. It seems like they are counting turnovers twice, that's why the pace is so high and the turnover rate is nearly twice as high as it should be. I wrote two emails already to ESPN regarding this, but it seems like they are fine with giving out wrong informations.

They have corrected the pace issue in 2010 and 2011, but haven't gotten the turnover rate correct. Thus, it is clearly still not completely fixed.