There are a lot of new stats out there that paint very nice pictures of just how good a batter is. But, for all the awesomeness of WAR (Wins Above Replacement) and wOBA (Weighted On Base Average), they still have one flaw that we see in most stats. That is, they don’t tell you who is getting the hits when it matters most*.
That’s where WPA (Win Probability Added) comes in.
WPA isn’t necessarily an indication of how good a batter is, or how good they will be in the future (that’s where WAR and wOBA come in). Rather, WPA tells us how important a player’s contributions have been.
In short, at any given point in a game, a team has a probability of winning the game. In the first inning it is about 50 percent. If the Rays are winning by 12 runs in the 9th inning, that chance is 99.9 percent.
WPA tells how much that percentage changes from one play to the next. For example, if a player hits a home run in the 9th inning when the Rays are already winning by 12 runs, the WPA is not very much (that home run doesn’t mean much). But if the player hits a 3-run home run in the 9th inning when the Rays are trailing by two, the WPA would be huge (that home run is much more important). At the other end, if a player hits into a double-play in an important situation, that would be a negative WPA.
Think of it this way: if a player does something good (a basehit, stolen base, etc.), they will earn more points if it happens during a critical moment in the game. And if the player does something bad (strikes out, doesn’t get the runner over, caught stealing, etc.) they lose more points if it happens during an important part of the game.
We can then add those up for a player over the course of a season to see how important that player has been (you can read more about WPA here. And you can see WPA in action here).
First up, the hitters, here is their overall WPA…
WPA
Matt Joyce has been the most important bat in the lineup so far. His offensive production has contributed to 2.21 wins on the season. He is followed by Johnny Damon and Casey Kotchman. At the other end, Reid Brignac has killed the Rays offensively (unlike WAR, WPA does not consider defense).
Think of this as the guys that have helped the most or hurt the most. But there is a problem. Obviously, some players have more opportunities. Like RBI, much of a player’s success depends on how many opportunities a player has.
So let’s scale the WPA per 100 plate appearances and see who Read the rest of this entry »
