WPA and Grand Slams

3:26 PM EDT Wednesday, July 19 2006

I found out about an interesting site today called FanGraphs.com. It tracks an interesting stat called Win Probability Added (WPA). Here's how it basically works. To calculate WPA you first have to have the probability table for each unique game situation. The game situation is determined by the inning, the score, the runners on base. The table is formed by determining the percentage of time a team has won in that given situation.

For example, if you looked at every game where the home team is down by 2 runs, with 2 out and runners on first and second, you might see that the home team goes on to win 35% of those games (I just made that up, I don't have the actual table). Then, say that batter hits a home run, so the home team is now up 1 run, with nobody on and 2 out. Now that is a new situation, in which the home team might win 60% of the time. In that at-bat, the batter has just increase his team's chance of winning by 25%. Had he struck out in that at-bat instead of hitting a home run, he would have decreased his team's chances of winning.

WPA is an accumulated running total of how much you increase and decrease your team's chances of winning with each at-bat during the season. I think this stat is valid in the recent discussions about A-Rod value to the Yankees. As of today, here are the top 5 batters in WPA:

  1. Albert Pujols - 640
  2. David Ortiz - 354
  3. Derek Jeter - 324
  4. Jermaine Dye - 318
  5. Barry Bonds - 317

This seems pretty accurate to me, it is generally accepted that Pujols and Ortiz are the two batters contributing most to their teams. Interestingly, A-Rod's WPA is 52.3. So there your have it, emperical evidence that A-Rod is simply not doing enough to help the team win. Also, Randy Johnson's WPA is -105.7, whereas Chien-Ming Wang's WPA is 152.

Also, in reading about this, I was reading about the Ultimate Grand Slam, which is a walk-off grand slam with your team down 3 runs, which is 90 WPA, the most you can earn in one at-bat. This article points out that Roger Conner hit the first ever grand slam and it was an ultimate grand slam. Also, it gives the answer to a trivia question I have wondered about for a long time. Whose career HR record did Babe Ruth break? The answer is Roger Conner, who had 138 when he retired in 1897.

Posted in  | Tags Yankees, MLB

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1. does the WPA take into account outside factors like weather, ballpark size/dimensions,how late in the season is it? What about history against the pitcher or team?

Seams like there are a lot of other factors besides innings, runs, count, and baserunner

# Posted By tim on Friday, July 21 2006 at 05:20 EDT

2. Hello my name's Paul Barry too :) How strrange

# Posted By Paul Barry on Sunday, July 23 2006 at 06:21 EDT

3. Tim,

I don't think WPA has to account for outside factors, because I assume they don't correlate closely to wins and losses. Also, you don't also have those stats readily available for every situation ever.

# Posted By Paul Barry on Wednesday, August 02 2006 at 10:53 EDT

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