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David Pinto and fielding (November 10, 2003)

Posted 2:16 p.m., November 10, 2003 (#1) - UZR and PZR blueprint (homepage)
For those who want more information on how to separate pitching from fielding on BIP, I provided a non-technical blueprint for doing so.

I think that someone out of MGL, Tippett, Pinto and maybe others can shed some big light on this...

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PZR is the exact same thing as UZR, but from the pitcher's perspective.

To recap the ultimate UZR as quickly as possible: given
- the location of the batted ball
- the trajectory of the batted ball
- the speed of the ball
- the game situation (inning/score/base/out/count)
- the speed of the runner(s) and batter
- the batter's handedness
- the gb/fb tendency of the pitcher/batter
- the type of pitch thrown (fastball, curve)
- the surface of the park
- the dimensions of the park
- the climate that day
- teammates' positioning

how often do we expect a league average fielder to convert that batted ball into an out (for each possible combination of the above)? How often did our playerX actually get an out? The difference is his performance level above league average for that position. Now, MGL captures most, but not all of that. (And maybe there's more too)

Now, you do something very similar, whereby the pitcher gets the same variables being controlled for that are outside his control. So, given
- the game situation (inning/score/base/out)
- the speed of the runner(s) and batter
- the batter's handedness
- the gb/fb tendency of the batter
- the surface of the park
- the dimensions of the park
- the climate that day

how OFTEN did pitcherY allow a batted ball into each of the zones? How OFTEN does a league average pitcher allow a batted ball into each of the zones?

What are the league out-conversion rates in each zone, for each combination of the above? Call these the "array of subzoneOutRates"

Multiply this array against the frequency of pitcherY's array. Do the same for the frequency of the league pitcher array.

The difference is the pitcher's performance level in balls in play.

Following this process will validate (or invalidate) DIPS.
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