Using Defensive Rating (DefRtg) to Analyze the NBA Finals

Ray Allen (34) and Mario Chalmers (15) of the Miami Heat defend Manu Ginobli (20) of the San Antonio Spurs during the NBA Finals.

Ray Allen (34) and Mario Chalmers (15) of the Miami Heat defend Manu Ginobili (20) of the San Antonio Spurs during the NBA Finals.

“Defense wins championships” – we’ve all heard that phrase at some point in our lives. We’ve even witnessed that at times during this year’s NBA Finals between the Miami Heat and San Antonio Spurs. Yet, the quality of defense can often be subjective to the eye of the beholder, particularly if the outcome does not necessarily agree with the evaluation.

Dean Oliver, author of the book Basketball on Paper, devised a metric for measuring an individual’s defensive efficiency. In his book, Oliver discusses a statistic known as defensive rating (DRtg). This measurement estimates the number of points allowed by a player for every 100 possessions by incorporating stats on blocks, steals, and defensive rebounds. It also includes the amount of defensive stops a player caused through forced turnovers and misses not included in the boxscore stats previously mentioned. For these estimations, Oliver goes through a long and thorough list of formulas that come as close to objectivity as any other extensive defensive metric.

Rather than spending our time on the logistics of the formulas, let’s focus on NBA.com’s defensive rating (DefRtg) statistic, which tracks the amount of points per 100 possessions a player’s team allows while that player is on the court. The rating is simple: the lower a player’s DefRtg, the fewer amount of points scored by the opponent. This statistic typically does a good job of evaluating a team’s performance and the probable outcome. However, as you’ll see from the game-by-game breakdown, the human element and general nature of the sport (along with some data limitations) can override statistical inferences.  Let’s take a look at the defensive ratings for the NBA Finals thus far, with the Spurs leading the series 3-2.

*Note: For this article, we’ll only examine DefRtg statistics for players who played a minimum of ten minutes per game to avoid data skewing.)

Game 1

The Heat were led by Chris Andersen (87.9), Mario Chalmers (93.0), Udonis Haslem (97.7), and Mike Miller (98.6) while Kawhi Leonard (95.8), Tim Duncan (97.5), and Gary Neal (98.1) led the way for the Spurs. Based on these numbers, it’s reasonable to assume that Andersen and Chalmers’ defensive impact led to a Heat victory. However, thanks to Tony Parker’s miraculous shot with .1 seconds left on the shot clock, the Spurs won Game 1 92-88. Interestingly enough, most people would even say that the Heat played good defense on Parker’s game-sealing shot.

Game 2

The Spurs were led by Tiago Splitter (98.8); their next player with the lowest rating was Danny Green with 116.4. Mario Chalmers (81.1), Mike Miller (83.2), Ray Allen (87.6), LeBron James (88.9), Chris Bosh (94.6), Dwyane Wade (97.7), and Udonis Haslem (98.9) were all phenomenal in their defensive efforts. The Heat routed the Spurs 103-84.

Game 3

Tiago Splitter recorded a remarkable 63.4 rating while playing over 23 minutes in Game 3. His teammates did their job as well; Tony Parker (78.8), Kawhi Leonard (83.4), Danny Green (85.3), Gary Neal (92.8), and Tim Duncan (98.8) all did an exceptional job limiting the Heat in route to a 113-77 embarrassment. The Heat player with the lowest DefRtg score was Udonis Haslem with 115.3.

Game 4

The Heat bounced back with six players leading the way: Norris Cole (83.3), Udonis Haslem (85.4), Ray Allen (93.5), Dwyane Wade (96.3), Mike Miller (96.7), and Chris Bosh (98.0). The Spurs returned to their Game 2 form with only Boris Diaw (98.0) scoring below 109. The Heat coasted to a 109-93 victory. One thing worth mentioning: Shane Battier saw an increase in action and recorded a 65.1 in almost 9 minutes of playing time.

Game 5

Even though the teams combine for the highest single-game point total, the back-and-forth cycle continues. Tiago Splitter led the way for the Spurs with a DefRtg of 65.8, followed by Gary Neal (68.2) and Manu Ginobili (96.5). Mario Chalmers led the Heat with a score 108.6; Shane Battier was next with 115.4. The Spurs held off a couple of Heat rallies for the 114-104 win in the pivotal Game 5.

As we see from the data, defensive ratings can be quite useful when evaluating an individual’s impact on an opponent and the outcome. Understanding the statistics behind a player’s defensive efforts is critical, but the human element can still trump those measurements. Notice that LeBron James, widely considered one of the best and most versatile defenders in the game, is only mentioned once in the game breakdowns above. Is this because LeBron is often guarding the best scorer for the Spurs? Or, is LeBron playing a large amount of time with weaker defensive teammates who are allowing the Spurs to score more, thus increasing his DefRtg score? These are data limitations that exist as of right now. However, the defensive ratings have shown credibility in accurately depicting the winner in 4 of the 5 games so far, with the only exception being the Game 1 nail-biter. The DefRtg statistic is doing exactly what statistics are supposed to do: provide information that leads to the most probable answer.

*Data and information gathered from stats.nba.com and basketball-reference.com

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Mark Simmons is a graduate student at the University of Central Florida, where he is earning a Master in Business Administration and a Master in Sport Business Management. Mark invites you to reach out to him on his Twitter and LinkedIn.

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