WPA helps explain Angels' struggles



WPA helps explain Angels' struggles

The Angels' Josh Hamilton leads the major leagues in negative WPA, a sabremetric statistic that calculates how clutch a hitter has been.

Most sabermetric statistics ignore context in favor of overall performance.

Even wins above replacement, or WAR, the supposedly all-encompassing sabermetric stat, is essentially blind to the things outside of a hitter's control – i.e., the situation in which he came to the plate. WAR thinks a leadoff homer is exactly as important as a game-ending homer, as long as the latter is solo.

But not "win probability added." WPA is all about in-game situations, calculating how much better of a chance of winning a player gave his team. On a game-by-game basis, it's a good way to understand who starred and what play was the turning point. Over a full season, it can tell you who was clutch and who wasn't – who hit well in tight games and who hit well when the game was already decided.

It's important to know and note, though, that WPA is not very effective at predicting the future. It's more of a look-back-and-understand stat – not a look-forward-and-expect stat.

So what exactly is it? Imagine that the score is tied 0-0 and the Angels have exactly a 50 percent chance of winning a game when Mike Trout comes to the plate in the first inning. (And that chance is quantified based on years of historical data covering alike situations.) Trout then hits a solo home run, giving the Angels the 1-0 lead and raising their chances of winning to 65 percent.

For that power display, Trout gets .15 WPA because he raised his team's chances 15 percent. If, in his next at-bat, he grounds out with two runners on and lowers the Angels' chances 10 percent, he loses .10 WPA and brings a .05 WPA into his next at-bat. The number can go up or down.

Most at-bats account for small amounts of WPA – positively or negatively – but there are also big-time chances. If Trout comes up with two outs in the ninth inning and the Angels down two runs with two runners on and he hits a game-ending home run, he would gain something like .70 WPA for raising his team's chances from 30 percent to 100.

League leaders generally add 5 or so WPA over a whole season. Trout's 5.32 mark in 2012 led baseball, according to That site charts every player's positive, negative and overall WPA each day

And here's where it gets really interesting: Guess who leads MLB in negative WPA this season?

Josh Hamilton. Guess who's fifth? Mike Trout. Guess who's 10th? Howie Kendrick.

The Angels have three of baseball's least clutch hitters, according to one credible statistical measure. No other team has more than one. Is that the end-all-be-all for why this team is struggling this season?

Not at all. Trout has also added a lot of positive WPA, enough to tie him with Prince Fielder for the 28th-best overall WPA.

But it's worth noting. And remember: WPA can't predict the future, so this could turn around soon.

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