Weighted Field Goal Percentage, Part 2

Posted: March 6, 2013 by nunuspeaks in NBA Mock Draft 2012

Ok, so we got some solid feedback on our post yesterday, in which we introduced a new metric for assessing total shooting performance.  Two of the most compelling points we felt the need to address are 1) Why are you counting 3 point misses against players more than 2-point misses?  and 2) What are the top 10 players in the NBA in terms of your new metric, Weighted Field Goal Percentage, and do your results pass the common sense test?  We’ll address both these questions below.

1) Why are you counting 3 point misses against players more than 2-point misses?

The simple answer to this question is that we are giving players extra credit for made threes.  If we put “bonus credit” in the form of heavily-weighted three point shots into the numerator of our equation but do nothing to the denominator (bottom-half) of our equation, we encounter the “Derrick Rose Effect,” which is the phenomenon of being better than perfect (110%).  The entire premise of our system is that metrics that tell you a guy’s “Effective” or “True” shooting percentage is 110% have told you very little, on top of being just plain confusing.

Let’s go back to our J.J. Redick example from yesterday.  Redick shot 9-10, including 3-4 from the free throw line and 5-6 from the three point line.  If we were to treat a 3-point shot attempt as equal to a 2-point shot attempt but also give extra credit to Redick for his made three’s, then our metric would feature the very flaw it was designed to correct: Redick’s WFG% would be 108%.  We are sympathetic to the idea that this is “unfair” or that a missed two is the same as a missed three (though we are actually skeptical of this in terms of the effect of a missed three vs. a missed two in an actual game, but we leave that aside).  But arguments can be made, for example, that a guy who jacks up bad three’s (pick your favorite example, mine is J.R. Smith) should be penalized for those shots.  We don’t necessarily advance that argument, though.  Our point is simply this:  if you want threes to count more when you make them, they will have a corresponding effect on your shooting percentage when you miss them.  We admit that’s not a perfect solution.  But we think it’s more useful and closer to the “truth” than a metric that routinely allows for better than perfect scores.

Nash leads among best 3-pt shooters in terms of WFG%

Nash leads among best 3-pt shooters in terms of WFG%

2) Who are the top 10 players in the NBA in terms of your new metric, Weighted Field Goal Percentage, and do your results pass the common sense test?

This is trickier, for the simple reason that we don’t know how to predict who would top the WFG% list without crunching the numbers of basically everyone.  But thankfully, we can use a reasonable proxy.  Our Weighted Field Goal Percentage basically weighs conventional field goal percentage, free throw percentage, and 3-point percentage and comes up with a number that reflects all three scores.  So let’s take a look at the league-leaders in one of those categories and see who tops the list.  Let’s use 3-point shooting percentage.  So if you look only at 3-point shooting percentage, here are your NBA league-leaders:

1.  Kyle Korver 46.2%

2.  Martell Webster 45.2%

3.  Stephen Curry 45.1%

Jose Calderon 45.1%

5.  Steve Novak 44%

6.  Shane Battier 43.6%

7.  Danny Green 43.5%

8.  Ersan Ilyasova 43.2%

9.  Steve Nash 43%

John Lucas 43%

Now let’s take the season FG% and FT% of each of these shooters and factor them in, using our WFG% metric.  Here is our new list:

1.  Steve Nash.  50.7% WFG

2.  Martell Webster.  50.2% WFG

3.  Jose Calderon 49.4% WFG

4.  Stephen Curry 48.5% WFG

5.  Ersan Ilyasova 47.8% WFG

6.  Kyle Korver 47.7% WFG

7. Danny Green 46.7% WFG

8. Steve Novak 44.1% WFG

9.  Shane Battier 43.7% WFG

10.  John Lucas III 42.4% WFG

So, does our re-imagined top-10 list “pass the common sense test”?  We think so.  If nothing else, we have another tool to use to take a closer look at the game.

-C. Smith @nunuspeaks

  1. Wilson says:

    … I still don’t see why you take issue with an eFG% or TS% over 100%. You’re playing a semantics game, in my opinion. I have a few problems with both posts.

    1. You fail to understand TS% differentiates between a made two and a made three simply by not differentiating between a two point attempt and a three point attempt. Which is also what eFG% does. eFG% does it by putting a multiplier on three-pointers made; TS% does it by using points scored instead of a multiplier on makes.

    2. As another person who left a comment tried to explain, eFG% and TS% are not literally shooting accuracy percentages. I’d probably describe it as a percentage/ratio that uses a player that only shoots twos as a baseline measure. For example, when JJ Redick shoots an eFG% of 115 on ten shots, it merely means he was 15% more efficient than a player who took 10 two-pointers and hit all of them. It’s not even that abstract a concept; JJ Redick shot more efficiently that night than Dwight Howard ever could.

  2. Art says:

    The inherent problem with WFG% is that the actual number itself doesn’t tell you anything. Neither does FG%. What does a .400 WFG% tell you of a player if he took 100 FGA?
    I KNOW a .400 eFG% tells me that if a player took 100 FGA, he’d score 80 points from those FGA. I KNOW a .400 TS% tells me that if a player took 100 FGA and 20 FTA, he’d score about 87 points.

    Even if eFG% or TS% is above 1, it just means that the player is so efficient from that he scores more than 2 points per FGA or TSA. What I don’t understand is the arbitrary weighting of 3/9 and 6/9 (and it could be simplified to 1/3 and 2/3) when you seem to attack TSA because it uses a weighting of .44 which is for the most part widely accepted in the APBR community.

    Finally, we would expect good shooters, that is players with high TS% and eFG% to be at the top of most shooting percentage lists, so the fact it passes the common sense test doesn’t mean anything.

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