Get To Know An Advanced Stat: Offensive/defensive rating

Over the course of the season, I'll be looking at an advanced stat every week in an effort to help basketball fans who may be timid about jumping into the stats pool head first.

First up, I'll dig into simple offensive and defensive rating (a metric that isn't all that advanced but falls under the 'advanced' umbrella because it's still foreign to most fans) to explain why looking at teams' points per game and points allowed per game numbers have almost become useless.

If you're already rolling your eyes, no worries, Knicks coach Mike Woodson "prefers raw points allowed over possession-based stats, anyway," we learned in a Grantland piece last month, and that's a much bigger problem than just a fan not wanting to adapt.

The basis of the criticism against raw points per game and points allowed per game in evaluating team offense and defense is that it can be greatly affected by pace of play. A team that plays up-tempo and therefore gives itself more possessions over the course of a game has a greater chance to score more points, while also likely allowing more points by giving the opposition more offensive possessions. But playing fast and the plethora of possessions that result from it doesn't make a team a great offensive team or a poor defensive team.

For example, last season the Bucks finished 12th in the NBA with 98.9 points per game, a seemingly solid offense. But that number was largely guided by the fact that Milwaukee's offense operated at the third-fastest rate in 2012-13, averaging 97.3 possessions per game. Their offensive rating, which measures points scored per 100 possessions, told the real story however. The Bucks averaged just 100.9 points per 100 possessions, good for 21st in the league.

On the opposite end of the spectrum, New Orleans provides a great example from last season of why points allowed per game is now mocked by fans, media members and basketball people who have adopted advanced stats. The Hornets (that was still their name last season) finished in the middle of the pack (14th) by allowing 97.9 points per game, which seems like at worst an average to mediocre defense. But they were actually the slowest playing team last year, with just 90.9 possessions per game, which kept their raw points allowed numbers down despite the fact that their 107.6 points allowed per 100 possessions, their defensive rating, revealed an awful 28th-ranked defense.

Basically, points scored and points allowed are way too dependent on the pace of play and therefore inadequate in their attempt to properly evaluate how well an offense or a defense functions.

Now I know many people fall back on simple team field goal percentage and opponents' field goal percentage, and looking at those numbers is far more reliable than points scored and points allowed, but there are still significant flaws here.

Remember that a possession doesn't end until possession of the ball switches teams, so you can go down the court, miss a bunch of shots, continue to grab offensive rebounds before scoring and still be scoring two or three points on that single possession. And if that possession included two points on three field goal attempts for a 33.3 percent shooting percentage, it's still two points per possession, and that's pretty damn efficient. Similarly, if on defense you hold a team to 40 percent shooting but you fail to close out defensive possessions with rebounds and therefore give up too many second chance points, did you really have a good defensive night?

The other thing that offensive/defensive rating takes into account is fouls and free throw shooting. Getting to the line is all part of a possession (the ball hasn't switched teams yet), so shooting the ball horribly but getting to the free throw line and scoring that way can still make for an efficient offense, just as holding a team to poor field goal percentages and rebounding well on defense can all be undone if you continuously bail the other team out by fouling and putting them on the free throw line.

What makes offensive/defensive rating so reliable and so effective compared to simpler and more dated measures of offense and defense is that it takes into account all that goes into an offensive possession or a defensive possession. Great defense is about holding offenses to poor shooting numbers while keeping them off the line and closing defensive possessions with defensive rebounds to give your team possession. Great offense is obviously about having good shooters, but it's also about having efficient scorers who can get to the line and big men who can keep possessions alive with offensive rebounding. This stat gets all of that. Points scored per game or field goal percentage allowed doesn't.

Mike Woodson can go on relying on his dated measures of evaluation (As much as anything Woodson's insistence on points allowed versus possession-based stats is probably just a cop-out for the Knicks' poor defense and their slow pace), but a lot of us now know better, and after reading this, I hope you do too.

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Get To Know An Advanced Stat: Offensive/defensive rating
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