One of the objections I heard today to my suggestion that Troy Tulowitzki deserves MVP consideration is that there’s a massive gap between him and Joey Votto in WPA. And it’s true, there is. Votto has the highest WPA in baseball, coming in at +6.47, while Tulowitzki’s +1.38 ranks him just 46th among position players, never mind all the pitchers who also rank ahead of him.
One of the main reasons why Tulowitzki’s WPA is so low is that a lot of his offense has come in games that had already been decided. In low leverage at-bats, he is hitting .361/.427/.649, but just .261/.357/.472 in high leverage situations. This gap is pretty large, and the opposite of Votto’s, who has hit better in high leverage situations this year. That makes a difference to a lot of people, and I understand why.
However, let me use an example from Saturday to show why you should be careful using context-dependent stats like WPA to determine how valuable a specific player was.
9/18, Colorado vs LA
Top 1st, 2 outs, runner on 1st, no score.
Tulowitzki hits a home run, giving the Rockies a 2-0 lead. Since their chances of winning jumped from 48 percent to 68 percent, Tulowitzki gets 0.20 added to his WPA total for the season.
Top 3rd, 2 outs, no one on, 2-0 Rockies.
Tulowitzki doubles to center. Because the Rockies were already likely to win the game, this double was worth a little less than a normal double, and he is credited with just 0.02 WPA. He would eventually score on Melvin Mora’s single, and the Rockies would take a 3-0 lead.
Top 5th, 1 out, runner on 1st, 3-0 Rockies.
Tulowitzki hits a home run, giving the Rockies a 5-0 lead. Because the Rockies already had an advantage, these runs were worth less than the earlier runs, so Tulowitzki only got 0.08 WPA for pushing their win expectancy from 86 percent to 94 percent.
I’d imagine you can see what happened here. Tulowitzki received minimal credit for his 5th inning home run because the Rockies already stood a really good chance of winning the game, and yet they had those good odds of winning because of what Tulowitzki did in his prior two at-bats. He essentially created his own low-leverage situation by single-handedly beating the Dodgers on Saturday.
Do you really want to say that Tulowitzki’s two-run homer in the 5th was less than half as valuable as his two run homer in the first? In terms of the story of the game, those runs didn’t have the same impact, but were they really less valuable? The fact is that the WPA of that HR is decided by how Tulowitzki performed in his first two at-bats of the game – should we hold a player’s good performances in less standing if they come after his previous good performances in the same game? Or, alternately, should we punish him for performing well on the same day that Jhoulis Chacin was throwing a shutout? If his first inning home run had tied the game, rather than breaking a tie, and his second home run had broken open a closer affair, the WPA story would be a lot different, even though the only variable we’re changing is the performance of the Rockies starting pitcher.
For these reasons, I lean towards context neutral performance. For me, WPA is like overall team performance – use it as a tie-breaker in a situation where it is otherwise hard to distinguish between two candidates, but don’t lean too heavily upon it. I’ll give Votto a bit of a boost for just how awesome he’s been in high pressure situations this year, but I’m not going to ignore how great Tulowitzki has been in situations where the game wasn’t close just because he helped make it not close in the first place.
WPA is great at telling the story of how a game unfolded. It is less great at evaluating how much a player helped his team win through his own actions. This doesn’t make it a bad stat, but it was designed for a specific purpose, and it is best used in that purpose. Trying to take it and turn it into a value stat for player performance is asking it to do something it was never intended for in the first place.
Dave is the Managing Editor of FanGraphs.