Mitch Keller Is Suddenly a Hot Commodity

There’s been a lot of chatter about surplus value around these parts in recent days. As Ben Clemens wrote last week, surplus value informs a large part of a given player’s appeal as a trade target. Count up all the projected WAR remaining on a player’s deal, multiply it by the price of a single win, subtract the remaining cost of the contract, and what’s left over is an estimate of the player’s surplus value. Anything less than zero, and the contract can be considered underwater; if a contract is underwater, a team seeking to offload that player would expect to receive nothing of value in a trade return.

A couple of months back, my assumption was that Mitch Keller’s contract was ever-so-slightly underwater. The right-hander inked a five-year, $77 million extension in February of 2024. His first year on that deal was thoroughly mediocre: He made nearly every start, but posted a so-so 4.25 ERA/4.08 FIP. Over the two years preceding the deal, it was much of the same. His 4.13 ERA between 2022 and 2024 ranked 68th out of 106 pitchers with at least 300 innings pitched; his 3.92 FIP ranked 51st. The strikeout and walk rates were nearly dead-on league average.

Is a roughly 2-WAR starter worth tens of millions of guaranteed dollars? Your mileage may vary. Patrick Corbin went to the Rangers for $1.1 million after posting a 1.8-WAR season last year. Andrew Heaney got two years and $25 million after delivering 2.2 WAR. Nick Pivetta, notably younger than both of those guys but still three years older than Keller, signed with the Padres for four years and $55 million. If Keller had hit the open market after the 2024 season, when he put up 2.2 WAR in 31 starts (178 innings), I’d imagine he would have received a contract similar to what Pivetta earned after his 2.0 WAR and 145 2/3 innings. Perhaps Keller’s deal wasn’t terrible, but it also wasn’t something teams would be dying to get on their books.

But now it’s the peak of trade deadline season, and the 29-year-old Keller is a hot commodity. The Pittsburgh Post-Gazette reported last Tuesday that the Blue Jays are in on Keller. That’s in addition to reported interest from the Cubs, Mets and Yankees. Nearly half of the most serious World Series contenders are in on the Keller sweepstakes, suggesting that contract is now perceived as having surplus value. Perhaps this has something to do with the haggard state of these teams’ rotations, but I’m inclined to believe that isn’t the entire reason.

My sense is that these teams would not be so hot on Keller’s tail if they saw him as a late-season innings eater destined to shift to bullpen work at the start of the postseason. Instead, they consider him to be more than quality depth. Or, in other words, the view him as a Guy.

So, is Mitch Keller a Guy now? On the one hand, he is posting a career-best campaign by both ERA (3.69) and FIP (3.44). On the other, his strikeout rate (18.8%) is the lowest of his career, and his fastball velocity is down over a tick from two seasons ago. This is not an unambiguous breakout.

If Keller is now a Guy, it’s because he’s unlocked a newfound ability to generate weak contact. And there’s nothing I like more than an investigation into whether someone is coming by their weak-contact generation honestly. He’s allowed just 10 home runs and a .286 BABIP. Is that luck or skill?

The first thing to know about Keller: He can really spin the baseball. He’s a lowish-slot supinator, and so it follows that his sweeper is the flashiest part of his profile. It can top 20 inches of horizontal break when the seams catch the air just right, making it among the most aesthetically pleasing pitches when it’s on:

He leverages his spin-first approach to construct an angular mode of attack. He’s not north-south, but he’s not exactly east-west either. It’s more like northwest-southeast, or southwest-northeast, depending on the handedness of the batter. Keller attacks the corners, forcing hitters to cover the entire plate at a wide range of velocities.

With the sweeper, as well as a more gyro-y slider, in the minds of hitters — plus a curveball and changeup he throws to lefties — Keller’s four-seam fastball plays above its subpar stuff numbers. Even with mediocre shape and average velocity, the heater gets hitters to swing super late. The average “attack direction” of swings against his four-seamer is over 11 degrees to the opposite field, ranking in the 81st percentile. Most of the fastballs that produce swings with this attack direction are fireballs — think Jhoan Duran or Daniel Palencia unleashing triple-digit bullets. Keller gets hitters to react late by forcing them to consider his bevy of spin.

Keller’s four-seamer has returned 1.4 runs per 100 pitches thrown, identical to Jacob deGrom’s heater. It’s been particularly tough on righties: Even though it misses hardly any bats (it has just a 8.8% swinging strike rate), righties are slugging just .218 off the pitch. His fastball induces a lot of groundballs tapped harmlessly to the right side:

Sadly, I was not able to access Stephen Sutton-Brown’s arsenal metrics in time for the publication of this article. But if I did, I’m almost positive that Keller’s scores would compete with those of any starter in the sport. His offerings touch all four quadrants of the pitch plot; meanwhile, he can touch 98 on the fastball and drop a 74-mph curveball into the zone.

As I’ve explored on a variety of occasions, pitchers with diverse arsenals covering large swaths of pitch plots can sustainably stay off barrels by preventing hitters from sitting on any one movement profile or location. But this isn’t the first year that Keller has featured a diverse arsenal. So what’s changed?

Keller struggled mightily early in his career, but after a velo boost in the 2022 season, he’s basically been the same guy: lots of spin talent, many pitches, theoretically-underwhelming-but-ultimately-effective four-seam fastball. If there’s an argument for Keller taking a leap from “decent pitcher” to “playoff starter on a team with championship aspirations,” it rests on some sort of explanation for his recent improvement in batted ball outcomes.

I’m not saying I’m convinced by this explanation, but Keller has made a pretty significant alteration to his arsenal from 2024 to 2025. Last season, he threw his cutter 12% of the time and his slider 9% of the time. Both pitches bled into each other from a shape perspective; neither performed particularly well. (Note the blurring of the yellow and brown dots on the plot below.)

The cutter, meant to be a soft contact option to lefties, instead allowed a .568 slugging on contact. The slider also got whacked around (-3.4 runs per 100 pitches thrown is about as bad as you’ll see on a given pitch type) and generated a below-average whiff rate in the process.

This year, he’s scrapped the cutter entirely. The more gyro-y slider still isn’t amazing; he’s allowing a .371 wOBA on contact with the pitch, and the whiff rate remains unimpressive. But canning the cutter and going heavy on the four-seamer to lefties has been a huge boon: His wOBA against lefties is .321 this year, by far the lowest mark of his career.

Is it that simple? Who knows. The easy answer is that Keller has improved slightly, but that makes for an unsatisfactory conclusion. I’ll come down hard with a medium-hot take and say Keller is mostly the same guy he’s always been. Would I give up serious prospect capital to pick up this contract for the next three-plus seasons? Probably not. If the expectation is something like a league-average guy for the length of that contract, I don’t know if it’s really worth it. Decent starting pitching can be found for relatively cheap; the Tigers just picked up Chris Paddack (and Randy Dobnak, currently in Triple-A) for a 35+ FV prospect. Keller is having a better year than Paddack, but they haven’t been all that different on a rate basis during their seven-year careers, though Keller has amassed 4.5 more career WAR than Paddack on account of his throwing nearly 300 more innings.

Still, how his trade value compares to Paddack’s this summer is of little concern to Keller. Really, why should he care what the Pirates get in return for him? From his perspective, all that matters is that he’s put together an excellent four months of baseball, and his reward will likely be high-leverage work for a competitive ballclub down the stretch and, potentially, in the playoffs.