I was looking at basketball reference and they use estimated points instead of actual points, but do appear to use 100 possessions as well. Basketball reference's offensive rating is 115 so the net ratingas aren't that different.
Yeah, both databases normalize to 100 possessions. OffRtg and DefRtg at nba.com AND at basketball-reference.com are based on 100 possessions. The way that these two databases arrive at the OffRtg and DefRtg metric is very different. At nba.com, Player X’s OffRtg is simply the number of points his team scores normalized to 100 possessions while he is on the court. Similarly, Player X’s DefRtg at nba.com is calculated as the number of points allowed by his team while Player X is on the floor, normalized to 100 possessions. That’s it. Simple. Easy to understand. But the OffRtg and DefRtg at basketball-reference.com is much more complex. See the following for complete details: http://www.basketball-reference.com/about/ratings.html. To calculate OffRtg at basketball-reference.com, one must solve the following equation: OffRtg = [Individual Total Possessions] / [Individual Points produced] x 100 In order to solve the first term of the equation above, you must first work through four preliminary equations to determine 1) Scoring Possessions, 2) Missed Field Goal Possessions, 3) Missed Free Throw Possessions, and 4) Turnovers. Once you’ve worked through those four equations, you may then determine the Individual Total Possessions for Player X. Then you must solve the second term of the equation; e.g., Individual Points Produced. In order to do this, you must first work through three more preliminary equations to determine 1) Point Produced via Field Goals, 2) Points Produced via Assists, and 3) Points Produced via Offensive Rebounds. Once you solved these three preliminary equations, then you will know the value of Individual Points Produced. Once you’ve solved the seven preliminary equations, and, know the value of Individual Total Possessions and Individual Points Produced, divide the former by the latter and multiply by 100 to get the OffRtg for Player X. IMO, this is overkill. The DefRtgs at basketball-reference.com are structured around Stops: primarily blocks, steals, defensive rebounds, forced missed field goals, and forced turnovers, and also involve a series of nine equations. Because big men are typically better rebounders and better shot blockers, they tend to receive better DefRtgs (lower numbers) than shorter/smaller players whose DfRtgs are artificially and systematically worse (higher numbers). Then there’s the naked eye and common sense. A database that suggests TJones (DefRtg = 105 via basketball-reference) and James Harden (DefRtg = 107 via basketball-reference), neither of whom is a good defender, are better defenders than Patrick Beverley (whose DefRtg is 108 via basketball-reference) fails the eye test. A database that suggest Eric Bledsoe and Markieff Morris are equally effective defenders is hard to believe. Eric Bledsoe is one of the best defenders in the league (his DRPM is +3.96, the highest of any PG in the league and the 13th best defender in the league at any position. Markieff Morris is not a good defender. His DRPM is -0.55, ranking 64th among the 88 PFs in this league and 247th in the entire league. How can you trust a database that awards both players a DefRtg of 106. It makes no sense. Finally, if you look at DefRtgs from nba.com, they tend to agree more with the naked eye than basketball-reference.com. For example, Patrick Beverley’s DefRtg of 101.8 at nba.com is the best of any Rocket player; a statistic that actually matches what we see with the naked eye. Let’s leave off the naked eye for a moment and look at other supporting evidence. The DefRtgs at nba.com more closely match the play-by-play video data at Synergy Sports as well. That’s why I trust DefRtg, OffRtg, and NetRtg via nba.com more than basketball-reference.com.
It's structured more around your team's performance, it's really got nothing to do with what you do block, steal, whatever wise after they dilute it, it's basically your team's defensive rating when you are on the court. It adds those other things, but they're so miniscule in effect, they're basically white noise (since the factors that make a good/bad defense, are the things they're adding to it)
I don't agree with this. Howard and Asik were better defenders last year by my eye test, but they play the same position. When Howard played with Lin, his defensive rating suffered more than when Beverley played with Asik.
fluors is right. What you're thinking of are probably the OffRtg and the DefRtg from nba.com which he also explained. The ORtg and DRtg from basketball reference (developed by Dean Oliver) are explained here (click), that's exactly what fluors wrote.
