APBRmetrics

[Guy]

[Eli W]

[Eli W]

[Eli W]

[Conan the Librarian]

I'm still waiting for somebody to explain to me how taking a shot attempt is a missed opportunity cost. Cause I still don't understand what else you're supposed to do with a possession.

[Guy]

Eli:
My point was simply that when opportunities are strongly correlated with position, then you will find a higher YTY correlation if you don't position-adjustment your values. What you want to know is how much of a player's Reb total reflects his rebounding skill, and how much it reflects his opportunities. If you don't account for opportunities consumed, using raw Reb totals is like evaluating a scorer based only on points, while ignoring FGAs (this is the irony in WP -- Berri makes the same mistake about rebounding that he has devoted thousands of words attacking on the scoring side). With rebounds, the first step in accounting for opportunities is a position adjustment. But there's also reason to believe that, especially on defense, there are large differences in opportunities even within positions.

Let me use a baseball example to illustrate. If we rated fielding based on outs made (putouts) per batter, the team total would exactly match team defensive efficiency. And we would also find a very high YTY r if we didn't position adjust, because there's a clear position hierarchy for putouts: 1B (c. 1400-1500), C (1,000), CF (410), 2B (350), LF/RF (320), SS (275), 3B (140). So we've apparently met both of Dean's conditions. But once you adjust for position, your YTY r will be much lower. Position-adjusted putouts tells you something, but it's far from a comprehensive defensive metric. (Catcher putouts, for example, are a function only of pitcher strikeouts and tell you nothing about the catcher's ability.)

[FrontRange]

[Eli W]

[HoopStudies]

[T.G. Randini]

I posted my final thoughts regarding Berri's overvaluation of rebounding at the WoW site:

THE SO-CALLED ART OF REBOUNDING: ON THE NATURE AND VALUATION OF CERTAIN POSSESSION TERMINATIONS IN BASKETBALL

There are many classifications, or typologies, of painting as art. Among them are classical art, impressionism, cubism, post-modernism, and dadaism (among many others). These various types represent different artist world-views, or, different ways of seeing the world. Below are presented various ways of looking at the valuation of rebounds in basketball.

#1: A Classical Approach to Valuation

Berri, Schmidt & Brook, in The WAGES OF WINS (2007, updated paperback edition) indicate on page 101 that opponents’ possessions are terminated five different ways: turnovers, made field goal attempts, made free throw attempts, team rebounds, and defensive rebounds. They indicate on pp. 248-249 (footnote 32 to Chapter 6)…

“We do not consider the impact of an opponent missing a field goal or free throw. When the opponent misses a shot the team can collect the defensive rebound, which we include in our evaluation.” …

“So opponent’s missed shot add nothing to our story.”

Okay… I beg to differ. It may not add anything to BSB’s regressions, but causing an opponent to miss a shot utterly DOES matter in the proper allocation of credit when terminating opponents’ possessions.

That’s the crux of the matter, isn’t it? How do we terminate the opponent’s possessions and how do we allocate the termination credits?

Under Berri, Schmidt & Brooks (henceforth, ‘BSB’) model… the allocation of credit (for missed shots) goes 100% to the person who fetches the ball after the opponent misses the shot.

Unlike BSB, I think the activity that terminates the possession is composed of two distinct elements:

Activity A: the causing of the shot to be missed
Activity B: the fetching of the ball after the shot is missed

Thus, (Activity A) + (Activity B) = Opponent Possession Termination

I believe that Activity A is just as important (if not more so) than Activity B… but for simplicity… let’s say they are equal.

Then, the allocation of credit for the total activity (activity A + activity B) would be as follows when valuing the possession termination due to a missed field goal (and utilizing defense as a team construct):

Point Guard .1
Shooting Guard .1
Small Forward .1
Power Forward .1
Center .1
Rebounder .5

The person who actual rebounds the ball would end up with .6, or 60% of the credit because .1, or 10% of the credit would be incremental to the 50% due to his team defense.

It would be easy to allocate credit in this manner: simply attribute rebounds as a .5 weight instead of a 1.0 weight to the rebounder… and then allocate the other 50% of individual ‘rebounds’ to a team pool (constituting team defense) and further allocate based on minutes played.

In this manner, you will more properly allocate “the causing of the shot to be missed” PLUS “the fetching of the missed shot”… instead of BSB’s attribution of 100% of the credit to Activity B, the person who fetches the ball.

Pertinent: The causing of the missed shot is an important activity because field goal percentages are almost always much lower than free throw percentages. If ‘causing the missed shot’ was not an important activity, then field goal percentages would be much higher and would reach equilibrium with free throw percentages. In fact, they could even exceed free throw percentages because you are forced to stand at least 15 feet from the basket when attempting a free throw. An un-defensed field goal could be as easy as a slam dunk or layup.

In summary to my classical approach to valuation… I believe a proper model would allocate credit to the skills employed in causing the opponent to miss a field goal attempt (and the fetching of the ball) instead of giving ALL the credit to the person who fetches the ball after the missed field goal.

Note: In answer to those who would say BSB’s ‘position adjustments’ would negate the effect of 100% attribution of (Activity A + Activity B) to merely the ball-fetcher (Activity B)… it wouldn’t… at least, not properly.

BSB’s methodology relatively overrates high-rebounding guards over lower-rebounding guards (and higher-rebounding forwards/centers to lower-rebounding ones). In effect, the BSB methodology overrates Jason Kidd compared to Steve Nash.

I shall not go into BSB’s conversion of a regressed .67 assist value to a .50 here, but will note that it is interesting they cite (p. 254, footnote 12 to Chapter 7, 2007 paperback) Hollinger’s three part deconstruction of a scoring play that is very analogous to my two-part deconstruction of a missed field goal/rebound, and then they complement themselves that their .67 regression value for an assist corroborates Hollinger’s intuition!

BSB, it is time you intuit the proper attributions of credit on the defensive side also.

Please note, the regressed value of the TOTAL activity (Activity A + Activity B) would be the same under my system as in BSB’s regressed value for Activity B alone. My system would not change the amount BSB’s regressed variables are ‘explained’ (using ‘explained’ merely in the academic statistical sense).

But my system would explain (capitalize EXPLAIN) what is going on a heck of a lot better than BSB’s attribution of 100% defense to the ball-fetchers. It would have the same statistically relevant explanatory power, but with the added enhancement of a much better way of attributing credit.

Explaining, instead of ‘explaining’.


#2: A Cubist Approach (to Valuation)

Let’s have a little more fun now. Let’s compare the ‘missed FG and rebound’ to baseball. In baseball, the batter is part of the offense, and the pitcher, catcher, and fielders constitute the defense.

The pitcher throws. The batter swings. Strike three. He’s out! Another strike out for Randy Johnson!

What happened here?

The batter (shooter) missed the ball (basket). The catcher caught the missed attempt. But the fans are cheering for Randy Johnson, the pitcher! What are they… nuts? The catcher caught (fetched) the missed attempt by the batter! Why are they not cheering for the catcher… (the fetcher)? (A mini-poem, sorry…)

Because the fans know something that BSB do not know. That defense is not 100% attributable to the ball fetchers and catchers.

The fans know that the speed, location, and spin of the ball by the pitcher (analogous to the movement and placing of basketball players when playing defense) constitute at least 50% of the value of getting the hitter to miss the ball when he swings (or the shooter missing the basket when he arches one up toward the rim).


#3: Another Cubist Approach to Valuation

I once watched the Dipper play tennis at a public park in LA in the late eighties. Great guy. Here’s the thing: Wilt was a graceful player. Two steps: forehand down the line. Three steps the other way: backhand down the line. Accomplished? Yes. And surprisingly graceful. (By the way, he was a track star in high school… and dberri, he did not like to be called ‘The Stilt’. He did like ‘The Dipper’, however…)

BSB (page 149, WOW, 2007 paperback edition) indicate that Wilt may have been responsible for 52-odd wins in the early 60’s when his team (the Warriors) won only 49 games. They, of course, see something wrong with this calculation.

If this calculation makes sense, the Warriors would have been better off if the other four guys did nothing at all! Just stand in a corner of the court and do nothing!

I love Wilt but he couldn’t do it all. Ergo: the Celtics dynasty.

The calculation is non-sensical because BSB attribute 100% of the credit to the rebounder for ‘making the opponent miss a shot’ + ‘grabbing the rebound of the missed shot’.

The attribution of 100% of the credit to Wilt for getting a rebound is what makes the 52-odd wins non-sensical… and by logical extension… … makes their attribution of credit in their Player Wins model non-sensical.

Dberri, there was a REASON for those four guys to be on the floor with Wilt.

(Note: Once again, I am saying BSB’s attribution of CREDIT is non-sensical, not the regression value for their mis-defined concept of ‘rebounding’ itself. The BSB regression value for (and terminology of) ‘rebounding’ is equivalent to ‘making them miss the shot + rebounding the loose ball’ in the construction I have presented above.)


#4: A Dadaist (and Final) Approach to Valuation

Let’s imagine a league where FG % is even worse than it is in the present NBA. (Heck, we could go back in history to the NBA itself… the 50’s… especially the early 50’s…)

Let’s imagine a 30% conversion rate. On average, the ‘expected outcome’ (sorry, people, that’s econ-speak)… would be negative for shooters.

A rational decision-maker (sorry again… more econ-speak), in this case, the coach, would instruct his players NOT TO SHOOT. “Don’t shoot!” the coach says to his team in the huddle. “Don’t EVER shoot!” Then, the expected negative outcomes through shooting would never occur, and his team would have lots of positive player win value through rebounding.

Except the other team’s coach is ALSO a rational decision maker and he instructs his team to do the same thing.

So… neither team shoots. Neither teams scores. The fans stop coming. The game of basketball dies.

All because BSB overvalue rebounding.


IN SUM: The above represents my thinking on the nature and valuation of certain possession terminations in the game of basketball as played in the late 20th and early 21st centuries using various classical, modernist and dadaist constructions (or dadaist ‘destructions’). Please consider the term ball ‘fetching’ as a dadaist intrusion into the classical and cubist schemes.

As Dorothy once sang in The Wizard of Oz…

Fetchers and catchers and bears, oh my!
The value of a rebound is much less than ‘pi’!

Always,
Tomas Giuseppe Randini

[Rasta978]

Randini,

Thanks for that interesting and entertaining post. I agree with your premise, but wonder about the added complexity that this would introduce into the various linear metrics. Also, do we have sufficient data to make this premise a reality?

A suggestion, though, on approach #4 (Dadaism). A league-wide decline in eFG% (and how the models deal with this decline) warrants deeper discussion. Your tongue-in-cheek prediction of "Don't Shoot!" ought to be fleshed out.

Consider, for example, my second favorite sport: soccer. Lots of similarities with the game of basketball, except that the eFG% (if soccer even bothered to track it) is probably less than 1%.

I'd be interesting is seeing how a dramatic decrease in eFG% would hypothetically play out. Which of our models, if any, would still be useful? And which would need to be scrapped, or at least revised?

[Mountain]

TG I put some comments in the what is a possession worth thread but obviously they bear on your post here and at Wages of Wins. I offered brief support for your posts there.

I may not get into it deeper right away but I hope more folks discuss the 'proper" or their preferred weighting between shot defense and fetching rebounds.

Right now I think net counterpart PER and Roland ratings deserve renewed attention given their inclusion of shot defense- and opponent rebounding.

[magicmerl]

I'm currently trying to get a response on WoW on your post (which was just dismissed out of hand).

[magicmerl]

And here that response is:

[asimpkins]