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Re: [APBR_analysis] Defensive ratings

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  • igor eduardo küpfer
    ... Hell, you didn t even mention the two biggest problems, IMO: I had to estimate both the FGM and OR terms, both in a way which penalizes big men. Anyway...
    Message 1 of 16 , Aug 30, 2004
      McKibbin, Stuart wrote:
      > Laid to rest? Okay. Here's a few theoretical problems I have with Ed's
      > approach, which on first blush sounds reasonable.
      >

      Hell, you didn't even mention the two biggest problems, IMO: I had to
      estimate both the FGM and OR terms, both in a way which penalizes big men.
      Anyway...

      > 1. A portion of the offensive ratings are earned in transition, say
      > the first 5 or 6 seconds after a steal or defensive rebound. This
      > favors the big men because it's the guards and SFs that do most of
      > the damage offensively in those situations in oddman rushes.
      ...
      > My proposal is that GETTING BACK is a team defense category and no
      > individual blame should be assessed. Everything that happens in the
      > first 5 or 6 seconds after a steal or def reb (provided there isn't
      > an interuption in play by timeout or something) should be taken out
      > of the equation. With the 82 games database this could be done.
      >
      > As it is http://www.82games.com/clock1.htm shows that teams give up
      > anywhere from 40-44% of offense in the first 10 seconds of a shot
      > clock. This could be further refined by changing the shot clock
      > segmentation (which would also eliminate such things as fouling
      > immediately to get the ball back, and stupid loose ball fouls by
      > attempted offensive rebounds that send the other team to the line
      > easily) and subtracting out all off reb putbacks and putting them in
      > a separate category. I would propose by removing those two things
      > we've isolated half -court offense and defense---which is what we are
      > really after, right?
      >

      As you note above, shot clock time does not equal possession time. About 30%
      of all missed shots are offensively rebounded, and therefore not subject to
      the "getting back" defense (GBD). Looking through a sample of 143 games that
      I have here, only 15% of all possessions end in under 10 seconds.

      Another thing is that of the offense recorded with 10 seconds or less on
      the shot clock, a lot of it comes on fouls at the end of games where one
      team fouls quickly to stop the clock. This too is not subject to GBD. Three
      percent of all possessions end in under 3 seconds -- I assume that these end
      in a player being fouled or a set play coming off an inbound or putbacks.

      That said, your points are well taken. I will see what I can do about
      analyzing my data more closely following your advice above.

      > 2. It doesn't take into account the variable offensive ratings of the
      > positions. Centers having lower average Ortgs than SGs and PFs, so the
      > centers as a group benefit again.
      >

      As far as I know, the difference here isn't all that great. Why don't I just
      check that? <sound of ruffling paper and pencil scratching> Hmm. It turns
      out that centers actually have *higher* offensive ratings, although the
      difference is not significant:

      POS ORTG
      1 102.0
      2 102.0
      3 102.2
      4 103.1
      5 103.5


      > 3. It doesn't take into account the team's defensive scheme. For
      > example, I'm told Boston did a lot of trapping of the PGs, so the
      > opposing PGs PER is lower than other opposing positions. I don't
      > think it's because Boston's PGs were exceptional defenders. Maybe
      > they were, I just doubt it. Or more to the point: Reggie Miller shows
      > up as superior to Ron Artest. That a 38-year old rates better than
      > the alleged Defensive Player of the Year is curious. In any event, I
      > wouldn't know how to account for it, so I'm just complaining without
      > a concrete alternative.
      >

      A standout example of a lack of strength-of-opponent factor in my system.
      Abdul-Rahim shows up on my top-20 list also, presumably for the same reason:
      neither of these players are asked to guard tough assignments. DanR's system
      is the only one, I think, that begins to address this problem.

      > 4. These rating systems are unfair to good perimeter defenders on poor
      > defensive teams.
      >.... It would take critical mass of perimeter
      > defenders (2, 3, 4?) to overcome their center's ineptitude.
      >

      An interesting idea.

      > So the options might be that only centers can be judged across teams,
      > and all we can do for the others is judge them relative to their own
      > team; or we give recognition for large relative decreases in pts per
      > 100 defense to perimeter players.
      >

      I never look at my defensive stats in isolation. I usually mix them with a
      heavy component of team defense, just to provide a safety net.
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