Subscribe!
CourtIntelligence powered by kenpom.com

The good stuff


At other venues...
  • ESPN.com ($)
  • Deadspin
  • Slate

  • Strategy
  • Whether to foul up 3 late
  • The value of 2-for-1’s

  • Philosophy
  • Brady Heslip’s non-slump
  • The magic of negative motivation
  • A treatise on plus-minus
  • The preseason AP poll is great
  • The magic of negative motivation
  • The lack of information in close-game performance
  • Why I don’t believe in clutchness*

  • Fun stuff
  • The missing 1-point games
  • Which two teams last lost longest ago?
  • How many first-round picks will Kentucky have?
  • Prepare for the Kobe invasion
  • Predicting John Henson's free throw percentage
  • Can Derrick Williams set the three-point accuracy record?
  • Play-by-play Theater: earliest disqualification
  • Monthly Archives

  • September 2014
  • July 2014
  • May 2014
  • April 2014
  • March 2014
  • February 2014
  • January 2014
  • December 2013
  • November 2013
  • October 2013
  • September 2013
  • August 2013
  • July 2013
  • June 2013
  • May 2013
  • April 2013
  • March 2013
  • February 2013
  • January 2013
  • December 2012
  • November 2012
  • October 2012
  • September 2012
  • August 2012
  • July 2012
  • June 2012
  • May 2012
  • April 2012
  • March 2012
  • February 2012
  • January 2012
  • December 2011
  • November 2011
  • October 2011
  • September 2011
  • August 2011
  • July 2011
  • June 2011
  • April 2011
  • March 2011
  • February 2011
  • January 2011
  • December 2010
  • November 2010
  • October 2010
  • August 2010
  • July 2010
  • June 2010
  • May 2010
  • April 2010
  • March 2010
  • February 2010
  • January 2010
  • December 2009
  • November 2009
  • October 2009
  • July 2009
  • February 2009
  • January 2009
  • December 2008
  • November 2008
  • October 2007
  • September 2007
  • July 2007
  • June 2007
  • May 2007
  • April 2007
  • March 2007
  • February 2007
  • January 2007
  • December 2006
  • November 2006
  • October 2006
  • September 2006
  • August 2006
  • July 2006
  • June 2006
  • May 2006
  • April 2006
  • March 2006
  • February 2006
  • January 2006
  • December 2005
  • November 2005
  • October 2005
  • September 2005
  • August 2005
  • July 2005
  • June 2005
  • May 2005
  • April 2005
  • March 2005
  • February 2005
  • January 2005
  • December 2004
  • November 2004
  • October 2004
  • September 2004
  • August 2004
  • July 2004
  • June 2004
  • May 2004
  • April 2004
  • March 2004
  • February 2004
  • January 2004
  • December 2003
  • November 2003

  • RSS feed

    “3-point defense” should not be defined by opponents’ 3P%

    by Ken Pomeroy on Thursday, December 6, 2012


    Saturday night, somebody noticed that Saint Louis had a horrible defensive 3P%. The first effects of the post-Rick Majerus era, right? Not really. It’s because the defense has little control over its opponents’ 3P%. As an illustration, let’s look at the best and worst “three-point defenses” in previous seasons on December 4th, and examine how they fared the rest of the season.

    What I’ve done is taken both the top 20 and bottom 20 teams in opponents’ 3P% as of 12/4 each of the last four seasons, and recorded their three-point defense from December 5th onward. All figures are averages for the 20 teams in each group.

              Thru 12/4             After 12/4
          Top 20   Bottom 20     Top 20   Bottom 20   
    2012   45.2       23.8        34.8      32.9                   
    2011   44.6       24.7        34.6      33.3
    2010   45.1       24.6        35.4      34.0
    2009   44.5       23.9        34.3      34.2
     Avg   44.9       24.3        34.8      33.6
    
    

    So on average over the rest of the season, there will be a roughly a 1-2 percent difference between the teams currently in the top and bottom 20 of opponents’ 3-point percentage. We’re talking about a difference of one make every two or three games between the best and worst groups. Without more analysis, one can’t say precisely how much skill a team has at influencing its opponents’ three-point percentage, but there’s a fair amount of evidence it’s not much, and even end-of-season figures are the result of significantly more noise than skill.

    With few exceptions, the best measure of three-point defense is a team’s ability to keep the opponents from taking 3’s. This is what the Majerus defense did, and fortunately for Billiken fans, Jim Crews is carrying on that tradition as SLU is currently allowing the nation’s second-fewest 3PA%.

    When people say that advanced-stats users are a bunch of nerds, I can only think the people that don’t use them are the real dorks. Nobody with any knowledge of the game would talk about free throw defense using opponents’ FT% as if it was a real thing, yet we’ll hear plenty of references to three-point defense in that way from famous and respected people. Of course, both free-throw defense and three-point defense exist, but it’s much better measured in the amount of shots taken and not in the noisy world of the percentage of shots an opponent makes.

    For reference, here’s a rough analysis of how well various team shooting stats currently identify greatness (or awfulness). The left column is the 12/4 difference between the average of the top 20 and bottom 20 in each category, and the right column is the difference between the same groups of teams ove the rest of the season. Essentially, the larger the difference going forward, the less noise the stat contains. Only data from last season is used in this comparison.

                Pre 12/4      Post 12/4
                  Diff           Diff   
    Opp FT%       19.7            1.7
    Opp 3P%       21.4            1.9
    Own 3P%       21.7            3.6
    Opp 2P%       20.9            4.8
    Own 2P%       19.6            5.5
    Own FT%       22.1            8.5
    Opp 3PA%      20.7            9.7
    Own 3PA%      24.1           14.5 
    
    

    When someone discusses three-point defense in terms of three-point percentage, they might as well make the leap to discuss free-throw defense in similar terms. Teams have much more control over how many three’s their opponents shoot than how many they make.