Year in Review: Twins Hitters WPA
by, 09-25-2012 at 10:12 AM (887 Views)
Oddly, a lot of sabrmetric geeks I know don’t like the Win Probability Added (WPA) statistic. I don’t want to speak for them as to why, but the comment I hear that drives me the craziest is something like “All you have to do is see that Erik Komatsu was more valuable then Ben Revere to understand that it is worthless.”
It drive me crazy because 15 years ago, I would hear the same question from baseball traditionalists when I’d suggest that an on-base machine like Bobby Abreu was more valuable than a guy with 20 more RBI. And I would say “Yes, that’s exactly what that means.” And I felt confident because:
- wins for a team correlates closely with run differential and
- the runs a team scores mirrors closely their On-base Plus Slugging (OPS)
- and a team’s OPS built is on their players’ OPS and
- Bobby Abreu has a crazy good OPS.
And they would say, “That’s nice that you have all those correlations and stuff, but Abreu only had 79 RBI last year!” They might agree with the method, but couldn’t accept the results. To me, that’s just being closed minded.
Similarly, I believe in the method of computing WPA. Here’s how it works:
- Analyzing dozens of years of baseball, you compute every game situation and how often a team in that situation won or lost the game. So, for instance, a home team that has runners on the corners and one out and is down by a run may have won games 55% of the time.
- Give the batter and the pitcher credit for how much they change those probabilities. So if the batter bounces into a double play, and the percent chance drops to 30%, then the batter loses .25 points and the pitcher gains .25 points.
- Do this for every play of every game throughout the year.
It’s not perfect – it doesn’t take into account fielding. If also isn’t especially predictive. And a player who plays a lot has plenty of opportunities for negative scores as well as positive scores.
However, it also is not dependent on other players; the player who is on third isn’t affected by the batter who grounds into the double play. And it rewards players who make big hits – hits that change the course of the game. Finally, if you look at the players with the highest and lowest WPA at the end of the game, it is almost never a surprise. It lines up with who you, as a fan, thought the heroes and goats of the game were.
In fact, I have rarely heard anyone criticize the method. It’s fairly simple to understand and, though it means handling a lot of data, the logic is straight-forward and elegant. But the results…that’s a different story.
And that will be the case when you see the Twins WPA this year. Today we’ll start with the hitters and get to the pitchers next time:
I suspect few people have trouble with the top two names on the list. Willingham not only had an enormous positive impact in games amongst Twins, his is one of the highest in the majors. It is the 2nd highest, right now, in the American League, sandwiched between Mike Trout and Miguel Cabrera. (Actually, Cabrera is fourth. Edwin Encarnacion is in 3rd, .05 points above Cabrera.
And fifth in the AL belongs to the next name on that list – Joe Mauer. He’s currently above Prince Fielder but a few percentage points. For all the talk about how “clutch” Mauer might not be and how many double-plays he grounds into, Mauer has had an enormous positive impact on the Twins this year. Statistically, it’s not debatable.
On the other hand, I suspect some folks are going to have trouble accepting that Ryan Doumit and Ben Revere have, offensively at least, cost the Twins several wins. Statistically, both have been fairly strong, but overall, they’ve had a lot more negative impacts on games than positive impacts so far this year. Because of that, they rank lower than subs that aren’t even with the team any more like …. well, Erik Komatsu.
That doesn’t mean the statistic is worthless. It just means Revere (and Doumit) didn’t have the offensive impact that we would have like to have seen. Of this, I’m confident.