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Monday, October 31, 2011
RE24/boLI
As you guys know, I’m big on WPA/LI (aka Situational Wins), even if I can’t articulate it well enough. I’ll get there one of those years.
Similar to WPA/LI (which is the change in win expectancy by game state, divided by the leverage for that game state) is RE24/boLI (which is the change in run expectancy by the 24 base-out states, divided by the leverage for that base-out state).
One set of boLI numbers can be found here. Basically, the highest leverage is with bases loaded, and lowest leverage is with bases empty. You can get a double in either case, but the impact of your double will be felt more with the higher-leveraged state.
So, in order to put both PA on a level playing field, you “deleverage” it by divided the change in run expectancy by the leverage index for that base-out state. Or, so I thought.
I wrote this to Sean Forman (who calculated RE24/boLI on his site) with regards to a Tyler Clippard play:
Sean,
Ok, this is what I’m thinking. Let’s look at this event for Clippard:
game_id event_num inning date_game
ATL201105100 67 8 5/10/2011There’s runners on first and second, the LI for that base-out state is 1.94. A HR is hit, 3 runs score. The RE delta is -2.38. We would divide that by 1.94 to “neutralize” the leverage.
However, part of that RE delta is the batter himself. He himself is not part of the “extra” leverage. His HR would contribute exactly -1 run to the delta RE regardless of what the boLI is.
So, what really should happen is that you divorce the delta RE between the runners and the batter. The neutralizing of the delta RE should only apply to the runners, not the batter.
I still haven’t thought through it all, but this is where I’m coming from.
I’ll talk to you later.
Tom
So, in the case of my Clippard HR illustration, the -2.38 RE delta was really -1.38 for the runners and -1.00 for the batter. We deleverage the runners by a factor of 1.94 (to get it to -0.71), and we leave the batter untouched (at -1.00), for a total deleveraged RE24 of -1.71.
Compare that to -2.38/1.94= -1.23.
I’m 90% convinced I’m right, but I’d like to hear from the Straight Arrows among you.
(And, if you had questions regarding deleveraging, be it here or with WPA/LI, now’s your chance as well.)
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