THE BOOK--Playing The Percentages In Baseball

Thursday, April 10, 2008

The Visual WPA Project

We’ve talked about something like this in the past, but we’ve never done anything about it.  Eric wants to give it a go.  I will also reproduce all my emails to him, for those interested in what I had to say:

I posted this on my blog the day after the game, and reprinted it here: http://www.hardballtimes.com/main/article/crucial-situations

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If you’ve got video of that game, you could do better in terms of splitting the fielding/pitching aspect.

Alot of those balls were hard hit, and the fielders for the most part had not chance at it (except for maybe Alou and definitely Gonzo).  So focusing on that would be a good thing.

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The other aspect you won’t get in the PBP is baserunning.  In a 1b to 3b on a single, we presume the runner will try for 3b about 30% of the time.  So, a single will automatically credit the batter with the runner being at 2b about 70% of the time and at 3b 30% of the time.  If a runner makes it to 3B, the runner gets the extra win value beyond the average win value of those two states.  If he stays at 2b, then he gets debited.  However, what if it’s a hardhit single to LF who was playing shallow?  Clearly, even Carl Crawford wouldn’t make it to 3B.  So, this would be a single where the runner would be at 3B 0% of the time, and the batter simply gets credit for a single that moves the runner exactly 1 base.  Similarly, what if it’s a deep single to RF, where even the slowest runner reaches 3B?  That gives the batter a 2-base single, and again, no credit to the runner.

Always try to break the play into states, estimate the chances of things happening from that state.

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The opposite applies to the fielding team.  How you wish to handle it is based on who is involved at the time the ball is in flight.

Let’s say that the win expectancy (WE) is .600 when the batter is at the plate.  The pitcher makes a great throw causing the batter to pop high in the infield.  99% of the time, it’s a sure out, causing the WE to go down to .550.  1% of the time, it falls for a hit, for a WE of .700.  The weighted average is .5515.

So, at the point of contact, you give the pitcher .600 minus .5515, or +.0485.  Now, after the point of contact, the pitcher is out of the equation and the shortstop is now in the equation.  If he catches the ball, the WE goes from .5515 to .5500.  If he doesn’t it goes from .5515 to .7000.

It’s all a matter of tracking what the win expectancy is, at the point that the player is involved.