Bucks Diary

Saturday, May 17, 2008

Defensive Win Score and the NBA All-Defensive Team


If you follow this blog, you will know that I have for some time believed you can pretty accurately quantify a player's defensive contribution to his team's success by simply taking Professor Berri's Win Score efficiency metric and rather than applying it to the player himself (as is custom), instead applying it to the player's collective "counterparts" -- ie those opponents he was assigned to guard throughout the season. I refer to this calculation as the player's "Defensive Win Score".

(The logic goes like this. If traditional Win Score shows how well the player did at producing statistics that correlate with victory, then Defensive Win Score should show how well the player did at preventing his assigned opponents from producing those same statistics... in other words, how well he played defense.)

Anyway, last night I painstakingly calculated the "Defensive Win Score" averages for each position on every team. They are in raw form, but this year's overall positional averages are listed at the top of every positional column. By subtracting the average from the team's positional total, and then multiplying by .20 (1/5th of all playing time) you can get an idea about the defensive win contribution each team received at each position. (note: you will notice the backcourt positions provided the Bucks with the most negative defensive win contribution of any backcourt in the NBA).

Click here for every team's Defensive Win Score averages by position

The Hidden Value of a Bill Laimbeer

Defensive Win Score is fundamentally different and broader than the traditional concept of defense. Traditional defensive evaluations myopically focus on "point prevention". But as the research in the book "The Wages of Wins" clearly demonstrates, there are many other components to victory. Defensive Win Score takes all of those various components into weighted account, and pays no mind to a player's "one-on-one" defensive technique, or shot blocking capability.

This technique leads to surprising, counter intuitive, results. Interior players who can force their counterparts to account for them on the perimeter of their defensive end -- players like Bill Laimbeer, Yi Jianlian, and Dirk Nowitzki -- have a hidden "defensive" value I never considered before I started calculating this statistic. By keeping the opposition's big men away from the defensive glass they simultaneously prevent one of the opposition's best "possession enders" from ending possessions. That can be considered a form of defense -- it extends their teams' offense.

That's why if you look at the numbers, Yi and Nowitzki both have excellent Defensive Win Scores, even though neither would be considered a "glove-like" defender by any standard. Both hold opposition power forwards well below their "per 48" rebounding averages. And once Yi becomes a better defensive rebounder himself, his advantage will multiply -- he will be on the defensive boards while simultaneously keeping his counterpart off the Milwaukee offensive glass. Maybe the idea of keeping Yi at power forward deserves a second look.

Defensive Win Score and the NBA All-Defensive Team

Based on my findings, I have to take two exceptions with the NBA All-Defensive team. Based on their Defensive Win Scores, I don't think Bruce Bowen or Marcus Camby deserve to be on the team.

In my mind, Bruce Bowen's value to the Spurs is significantly overstated. He is on the floor strictly for his defensive contributions, yet if you quantify those contributions according to Defensive Win Score, he actually makes one of the smallest defensive win contributions on the team (-0.082). That's just below average (with average being +0.000), but it goes without saying it is not up to All-Defensive team standards. According to defensive win contributions, which is equal to Defensive Win Score above average multiplied by the player's percentage of overall playing time, Bowen's spot rightly belongs to Paul Pierce, the NBA's Defensive Win Score "Player of the Year". (With a Defensive Win Contribution of +0.569, I estimate Pierce's defense alone added 4 more victories to the Celtic win column than the average player would have added in the same amount of playing time and given the same positions).

The second mistake selection based on reputation is Denver center Marcus Camby. By Defensive Win Score calculation he is one of the worst defensive centers in the game (-0.331)! His addition to the All-Defensive team is based, I'm assuming, on the mistaken belief that blocked shots equal good defense. They don't (necessarily). Focusing solely on Camby's blocked shot totals ignores the costly trade offs he makes to achieve those blocked shots.

By attempting to block everything in his sight, Camby effectively turns his counterpart centers completely loose. Indeed, when matched against Camby, NBA centers grabbed significantly more rebounds per 48 (particularly offensive rebounds -- supporting my "he turned them loose" hypothesis), shot a higher percentage from the field, and committed fewer turnovers.

And, there is no evidence Camby's shot blocking had any chilling effect at all on the other team's shooters. Denver's opponents had a better effective FG% with Camby on the court than they did with Camby on the bench.

That all being said (or written), here is the NBA All-Defensive team if I were choosing.

Bucks Diary's "Defensive Win Score" NBA All-Defensive Team

First Team

PG-- Deron Williams, Utah Jazz (dwc: +0.374)
SG-- Tracy McGrady, Houston Rockets (dwc: +0.471)
SF-- Paul Pierce, Boston Celtics (dwc: +0.569)
PF-- Kevin Garnett, Boston Celtics (dwc: +0.378)
C-- Dwight Howard, Orlando Magic (dwc: +0.484)

Second Team

PG-- Chauncey Billups, Detroit Pistons (+0.315)
SG-- Kobe Bryant, LA Lakers (+0.405)
SF-- LeBron James, Cleveland Cavaliers (+0.225)
PF-- Dirk Nowitzki, Dallas Mavericks (+0.326)
C-- Chris Bosh, Toronto Raptors (+0.329)

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