I Think Win Probability Added Is a Neat Statistic

We’re in a tiny lull in the baseball season, and honestly, I’m happy about it. July is jam packed with draft and trade talk, September and October are for the stretch run and the postseason, but the middle of August is when everyone catches their breath. There’s no divisional race poised on a razor’s edge, no nightly drama that everyone in baseball tunes in for; it’s just a good few weeks to get your energy back and relax.

For me, that means getting a head start on some things I won’t have time to do in September, and there’s one article in particular that I always want to write but never get around to. I’m not a BBWAA member, and I’ll probably never vote for MVP awards, but I spend a lot of time thinking about them every year nonetheless. When I’m looking at who would get my vote, I take Win Probability Added into account. Every time I mention it, however, there’s an issue to tackle. Plenty of readers and analysts think of WPA as “just a storytelling statistic” and don’t like using it as a measure of player value. So today, I’m going to explain why I think it has merit.

First, a quick refresher: Win Probability Added is a straightforward statistic. After every plate appearance, WPA looks at the change in a team’s chances of winning the game. We use our win expectancy measure, which takes historical data to see how often teams win from a given position, to assign each team a chance of winning after every discrete event. Then the pitcher and hitter involved in that plate appearance get credited (or debited, depending) for the change in their team’s chances of winning the game. Since every game starts with each team 50% likely to win and ends with one team winning, the credit for each win (and blame for each loss) gets apportioned out as the game unfolds. The winning team will always produce an aggregate of 0.5 WPA, and the losing team will always produce -0.5, spread out among all of their players.

That’s just tremendously neat. As the glossary entry for WPA puts it, “We know intuitively that a home run in the third inning of a blowout is less important to that win than a home run in the bottom of the ninth inning of a close game.” We do know that! But the argument against WPA is that thinking about the game that way doesn’t match what actually matters.

Here’s an example. Let’s say that the Giants are up 5-0 in the third inning when Joc Pederson hits a two-run home run. Win Probability Added: minimal. Then, the Giants cough up the lead and trail 8-9 headed into the ninth inning. Joc blasts another two-run bomb, this one decisive. Win Probability Added: massive. But since the final score of the game was 10-9, taking either two-run home run off the board would result in the team losing 9-8. Why are they treated differently?

That’s a compelling argument. If you imagine that the base/out state was the same both times, it gets even better. Both home runs were necessary for the Giants to win the game. One gets treated as nearly worthless by WPA, though, while the other is worth its weight in gold. You can make it feel even more unjust if different players hit the two homers. Joc the Irrelevant, Yaz the Hero? What, by virtue of when they did an equally important thing? Sure seems arbitrary when you put it that way.

Given how many baseball statistics there are in the world, you could account for that if you wanted. There’s WPA/LI, which adjusts every outcome for the leverage going into the plate appearance, so that how you perform relative to what was expected in each situation is what matters, not how important the situation was. RE24 uses run expectancy rather than win expectancy, so everything is on the same scale.

I don’t find those arguments compelling, however, because I think they misunderstand the contingent nature of a baseball game. Runs aren’t created equal. Timing matters. The game unfolds differently based on what has already happened; a team might put in their mop-up guy or go to their closer based on the game state. To reduce the argument to absurdity, consider last weekend’s Mets/Braves tilt. The Mets were down 13-3 heading into the ninth inning and thus sent a position player to the mound. The Braves promptly scored eight runs. Were those runs equally as important as the first eight of the game? I can’t imagine making that argument in good faith.

Here’s another way of looking at it. Imagine, if you will, that the Giants were on the road in our initial example. Further, imagine that they gave up a two-run bomb of their own in the bottom of the ninth to lose 11-10. Were Pederson’s two home runs each worthless to the outcome? Did they go from hugely valuable to of no import because of that subsequent event? That doesn’t feel right either.

The future is always unknowable. In my opinion, that means that evaluating one plate appearance based on how the game unfolded afterwards misses the point. Every time a hitter comes to the plate, all they can do to best help out their team is maximize that plate appearance. WPA handles that quite well, because it explicitly doesn’t care about what happens afterwards.

From a predictive standpoint, none of this matters much. A home run is a home run is a home run; you’re not going to get anywhere by treating different ones differently if you’re trying to figure out how good a player will be in the future. Decades of research have hammered that point home. That’s also true if we’re trying to measure a player’s underlying talent; there’s no evidence that hitters control when they hit their home runs. We all pretty much know that; there’s a reason that the single-season home run record is so famous while no one cares about “number of runners driven in via home run.”

If you want to know who the best player was in a given year, I think WAR answers that question pretty well. Is that what the MVP award is for? I don’t read it that way. Per an FAQ on the BBWAA website, the award considers “(a)ctual value of a player to his team, that is, strength of offense and defense” in addition to other clauses about games played, character, loyalty, and effort. To me, “actual value” carries a connotation that the particular circumstances of each event matter. What’s the “actual value” of a hit or a strikeout? The context in which it occurs surely has to matter at least somewhat.

How does that relate to WPA? I think it’s almost a direct translation. Players can’t control the situations they find themselves in; that’s one of the neat things about baseball. The batters in front of a player determine the base/out situation they face. All a player can do – all that’s in their control each time they step to the plate or face a new batter – is increase their team’s chances of winning that game by as much as possible.

If that sounds a lot like WPA to you, then you’re thinking about this the same way that I am. WPA doesn’t care about how you got there. It doesn’t care about what happens afterwards. It bores in on the individual situation and nothing else. How much actual value did a batter provide? I can’t think of a better way to encapsulate that than by starting with how the game looked before they batted and finishing with how it looked afterwards. Whether the team came back later, whether some future event cheapened or heightened their earlier contribution – that isn’t what we’re talking about here. How much did a player help his team? For me, that’s a close corollary to how much win probability they added.

I don’t mean to say that I won’t consider anything else when looking at who deserves to take home hardware at the end of the year. Sure, WPA sounds a lot like the MVP criteria to me, but it’s not a perfect match. “Actual value” is purposefully nebulous. A ton of home runs is a ton of actual value, even if a team squandered that value by not having baserunners on to capitalize. The same is true for someone who reaches base a bunch; if they end up disproportionately doing it in unfavorable spots because their team doesn’t cooperate, it’s hard to blame the player for it.

Quite frankly, a big disagreement between WAR and WPA doesn’t come up very frequently. This year’s WPA leaders in each league? Shohei Ohtani and Ronald Acuña Jr., the two MVP favorites. Last year’s? That’d be Aaron Judge and Paul Goldschmidt, who both took home the trophy. In 2021, Ohtani and Bryce Harper led their respective leagues, and both won MVP. For the most part, this statistic is telling us what we already know.

I hesitate to mention it, but WPA comes close to making me understand why RBI are still considered a key statistic by a lot of baseball fans. We know, again thanks to decades of research, that RBI aren’t a particularly skill-intensive statistic. They depend a lot on context; who’s on base when someone steps to the plate matters a lot more than the skill of the batter. But if you’re wondering who contributed to a game’s outcome, they’re undeniably important. You can’t win without scoring runs, and RBI inarguably produce runs. That’s why people still love them even though they aren’t predictive of future production or even descriptive of current talent.

In some senses, WPA is just a sharper way of measuring what RBI were attempting to capture. Driving that run in from third base with a sacrifice fly really does have value; it truly isn’t the same as a strikeout, at least in terms of winning the game at hand. But that’s less impressive than a solo homer in a different situation, or even a single to drive home the runner, and WPA can handle that range of outcomes much better than a single binary statistic (did the runner score or didn’t he?). WPA also considers driving a run home from second more valuable than driving one home from third, and doing so in a close game more valuable than doing it in a laugher. It’s what RBI fans think their statistic does. WPA also captures the other side of the coin, setting the table for future hitters, which is an equally important part of winning, and it handles it much better than a raw count of runs scored would.

So if you’re reading this and you’re an MVP voter, here’s my plea: take a look at win probability numbers when you’re compiling your ballot. It probably won’t change your vote, because as I’ve already mentioned, it mostly mirrors how MVP voting already goes. The best players tend to add the most win probability because, well, they’re the best players. But in corner cases and down-ballot tiebreakers, looking at who actually did the best with the opportunities they were given deserves a spot in the conversation. Don’t forget to sprinkle in a little bit of accounting for defense, as WPA only gives credit and blame to the pitcher rather than the fielders behind him, but how much defense matters in MVP voting has always been in the eyes of the beholder anyway.

If you’re reading this and you aren’t an MVP voter, I’d basically ask you the same thing. When you’re thinking about who helped their team out the most this year, spare a thought for WPA. It isn’t always the best at telling you who will be good next year. It isn’t always the best at telling you who was the most talented this year, even. But when you’re wondering who helped their team out the most – who came to the plate down and left ahead, who chiseled into deficits and slammed the door on leads – WPA does a great job of explaining exactly that.