Win Probability Added is one of those stats at the intersection of fun and not quite meaningful. Like RBIs or Wins, it is more of a story stat than one that has much value as a measure of overall performance. In short, it works like this... Over the millions of baseball games played, the odds of every scenario have been calculated: a team down by two runs with three innings to play comes back and wins X amount of the time. Say someone hits a double to open the 7th, that raises the chance of a comeback by however percent. So the guy who hit the double added, say, 2% to the teams chances of winning. For an example, here's the WPA data for Sunday's win over the Angels.
The quickest way to race to the top of the WPA leaderboard early in the season is to hit a home run in the 9th inning to win a game. Here are the team leaders in WPA thus far, totals are in percentages of a win:
Matt Treanor: .64 (Treanor!!!!!!!!)
- Chris Getz: .41
- Kila Ka'aihue: .33
- Wilson Betemit: .30
- Jeff Francoeur: .28
- Joakim Soria: .45
- Tim Collins: .44
- Jeff Francis: .33
- Aaron Crow: .23
- Nathan Adcock: .02
As you might guess from the pitcher list, after the top four, there hasn't been much overall good done. Everyone below Adcock (who was saved when the Angels ran into an out at home) has been a net negative in terms of win probability.
These numbers... well... they're numbers. More or less, they're just fun. Especially after four games. Wilson Betemit, for example, is riding high on one shining monment. His double in the 9th inning of Sunday's game raised the Royals' chances of winning that game by over 50%. Other than that hit, he's been a net negative thus far.