Best of BP: Kevin Gausman Is In Trouble

There are a number of reasons why a pitcher might attack the zone with their fastball, and I’m going to list very few of them. The most obvious is that their fastball is good, maybe great. Perhaps they can spot it well. Sometimes it isn’t about the fastball at all! It’s about the stuff the pitcher throws when they’re not throwing the fastball.

Here’s a list of starting pitchers, ranked by fastball zone percentage, since 2021:

1. Kevin Gausman, 2020
2. Kevin Gausman, 2024
3. Kevin Gausman, 2022
4. Jared Jones, 2024
5. Louie Varland, 2023
6. Zack Wheeler, 2024
7. Kevin Gausman, 2021

That’s Kevin Gausman, four times, over four years, in the top seven spots. No one attacks with their fastball like him, which is funny because, as far as pitch characteristics go, his fastball kind of sucks. By vertical approach angle, it’s about as generic as it gets. Induced vertical break, average. Spin rate, average. Velocity, a touch above-average. And all he’s done despite all of this is post the single-highest strike percentage of any starter’s four-seam fastball since 2019.

Here’s part of how he’s able to do that. Watch him dispatch Teoscar Hernández with a splitter:

This sets it all up. You already know this about Gausman. The concept is nothing new, or special. His splitter looks like a fastball, and then the bottom falls out and dives out of the zone. It’s what has made his fastball one of the best at generating whiffs at the top of the zone, and also one of the very best at getting hitters to take strikes at the knees. The splitter is what allows him to so aggressively attack the zone with heat, even though he disproportionately throws his splitter outside of the zone. They’re quite opposites, in that way.

There’s something to that. Gausman’s fastball is the very best of its kind at generating strikes, but, contrary to what you might think, his splitter is lousy when it comes to strike percentage. Like, one of the lowest of all pitches in MLB, especially this year. That’s not particularly surprising—zone percentage and strike percentage are closely correlated, and since 2021, Gausman has thrown his splitter outside of the zone more than any pitch from a starting pitcher in MLB. It’s not even close.

All of this is fine, so long as the splitter remains a weapon. As the argument goes, if a pitcher loses his splitter, he becomes pretty useless. But the counter-argument is that the volatility of splitters is overstated—which is perhaps why the league is moving towards them—and as pitchers age and lose velocity, that actually makes their splitters more deadly as they get more and more depth, because their movement and velocity differentials remain relatively identical to their fastballs. Of course, this is all theoretical, and quite possibly extremely wrong. But splitter guys losing velocity historically hasn’t worried me as it has others.

Gausman is now solidly testing this theory. Consider how well hitters are slugging against his primary offerings:

Hitters are slugging more than Kyle Tucker and Aaron Judge when Gausman throws his fastball, which is different from what they did before, which is slug like a very good, but not elite, hitter. Both are not quite ideal, but one is clearly worse, and it’s the one that’s happening now. Why this is, I’m not sure that I can say for certain. It doesn’t help that his average fastball velocity has dipped below 94 miles per hour. That’s something I know for sure. His fastball performs a lot differently above and below the 94 mile per hour threshold. But, as always, that doesn’t explain everything.

Here’s an elevated fastball to Freddie Freeman:

This pitch right here? Gausman is throwing it pretty much less than ever. He’s thrown the elevated fastball less than any year outside of 2015. And as far as vertical fastball location goes, he’s effectively averaging his lowest since 2019. That fastball above? It sets up the splitter to be thrown at the bottom of the zone, maybe below it, and probably for a whiff. More recently, Gausman has been doing more of this:

A strike! We love those, and we’ll take this outcome 10 times out of 10, but what it’s not doing is setting the splitter up. Hitters will go down and out of the zone to chase on a Gausman splitter, but they won’t always extend the zone too far—especially when the splitter isn’t being set up properly. Given the choice, I might take the fastball fouled away at the letters over the called strike above the knees. Not because of the outcome, but how Gausman is changing eye levels, showing something up so he can go back down.

And if it helps, here’s this idea more visually. Here, the average vertical pitch locations of Gausman’s fastball and splitter, and the difference between the two:

A few things stick out. The first is that, over the past few years, Gausman’s fastball has averaged below the vertical middle of the strike zone. Part of the reason that Gausman broke out years ago is that he learned to more consistently elevate his fastball. He’s reverted to his pre-breakout years. Shift your eyes over to the furthermost right column, and you’ll notice that Gausman’s best years are ones where he’s providing ample space between his fastball and splitter locations, vertically. The easiest way to do that? Throwing to the top of the zone more.

Still, there are enough oddities in Gausman’s numbers that I don’t think fastball velocity and pitch locations are sufficient explanations for his struggles. It makes sense that hitters might pick up Gausman’s fastball a little easier. But regardless of sequencing, regardless of location, the splitter ought to still dominate, just less so. We’ve seen the chases remain steady, but the whiffs have plummeted from 26.9% in 2022, to 22.2% in 2023, and now down to 17.0% this year. In particular, his in-zone swing and miss percentage has dropped precipitously, from 28.9% in 2023 to 14.5% this year—worse than his fastball’s 16.6%. That reeks of a pitch that ain’t right.

Check out Gausman’s splitter numbers, courtesy of Texas Leaguers:

Gausman’s splitter is changing. By expected movement direction, it’s remained about the same, but by actual movement direction, it’s started to shift more vertically over time. That means a more vertical pitch shape: by IVB, Gausman’s splitter has the most “ride” it’s had since 2017, which means it’s not quite getting the depth that it has for the bulk of his career. And his axis deviation (or, here, tilt difference) doesn’t necessarily mean he’s lost non-Magnus movement—axis deviation isn’t synonymous with seam-shifted wake!—but for a pitch that’s much more spin-efficient than not, that would be my best guess, if I were made to venture one. In other words, his splitter is moving more like you’d expect it to coming out of his hand.

If that’s the case, then the fix would be to get the splitter right, which would probably already be done if it was an easy tweak—there’s a reason not everyone throws a Gausman splitter. Since that won’t likely be restored any time soon, the focus ought to be the fastball. He’s already folded in a two-seam fastball, and he’s even toyed with a one-seam fastball at times, but right now, nothing would help him more than getting his fastball located around the letters with more regularity. Until then, his aggressiveness in the middle of the zone is being weaponized against him.

For just about ever now, Kevin Gausman has thrown his fastball for a lot of strikes, and his splitter for a lot of balls. More often, the fastball strikes are turning into balls in play, and more often, those balls in play are turning into extra-base hits, or worse. It used to be that the splitter would generate more whiffs than any pitch in baseball, in which you could deal with the misses. Recently, not so much, which means my theory that splitter pitchers age well is in jeopardy.