Measuring the defensive effectiveness of NBA teams?

Quantifying defense in basketball has been a sticky situation for analyst and fans for some time. In this post I will introduce a simple measure of the effectiveness of the defense of a given NBA team and use this measure to show the "defensive bias" of teams across the league for 2008-2009 and 2010-2011 NBA seasons. Hollinger's defensive effectiveness presents a measure for this team defensive effort. The focus will be on the defensive effort that changes the effectiveness of the opposing teams scoring.

The term "defensive bias" will be used to describe this measure of defensive effort. The first step in calculating this measure will be calculating the average scoring by the opposing (away) team in the last N games. avgscore

In the analysis of the data set the variable N for the number of games average will be set to 10. Once the average of the N previous games is calculated the current game's score is used to estimate the defensive bias of the home team using the following formula.


In a concrete example for the game Golden State Warriors at Los Angeles Lakers  (December 28, 2008) the scoring average for the last 10 games for the Golden State Warriors is calculated and weighted against the 113 that they scored on Dec 28.


This defensive bias was calculated for multiple teams in the 2008-2009 NBA season and averaged across the season. This analysis is summarized in the following chart.


From this analysis we observe that some of the suspected best defensive teams like the 2008-2009 Boston Celtics are among the leaders in defensive bias. The best 7 teams are as follows:

Boston Celtics

Los Angeles Lakers

Cleveland Cavaliers

Dallas Mavericks

Portland Trailblazers

San Antonio Spurs

Orlando Magic


The 2010-2011 NBA season was also analyzed to have another season to compare against the instincts of those following professional basketball.


The best 7 defensive bias teams in this season are as follows:

Chicago Bulls

Miami Heat

Los Angeles Lakers

San Antonio Spurs

Dallas Mavericks

Oklahoma City Thunder

Denver Nuggets


From this analysis we see the data display the success of the San Antonio Spurs defensive system and Tom Thibodeau's success with the Bulls in his first season.





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