It happens every fall, without fail: Some reliever gets red-hot, then his manager rides him beyond all reasonable limits because that’s what the situation demands – and yet he gets the job done so often, so regularly, that he helps push his team to greater heights, simply because that’s what October requires of you.
Sometimes that’s Andrew Miller (2016). Sometimes that’s Kevin Ginkel (2023). But it’s always someone. Last year at this time, we tried to look ahead and identify who those Relief Aces might end up being, trying to get a little deeper than just “the closer.” We named Cade Smith and Luke Weaver, who did indeed end up being the two most valuable relievers of last October. We also brought up Kaleb Ort and Keegan Akin, which is a good reminder that you can’t win them all.
Let’s do it again. No, we’re not talking about Josh Hader or David Bednar or Jhoan Duran or Andres Muñoz, because they’re big stars and the expectation is already there that they’ll be great. What about the non-closers? The names not everyone knows yet? The ones where expectations are lower? In no particular order, these are the relief arms to watch this time around.
Brad Keller, Cubs RHP
Key stat: Fastball velocity up 3.5 mph
Where do good relievers come from? Quite often, the answer is “other teams” and “where they had been trying to be starters.” That describes Keller, who spent parts of six seasons soaking up league-average innings for the Royals (105 ERA+, where 100 is average, between 2018-23), then spent 2024 with the White Sox and Red Sox, being designated for assignment by each team around a 5.44 combined ERA. That left him unsigned into late January, when he inked a non-roster invite with the Cubs.
Keller, having spent his winter working on some mechanical flaws, showed up at camp ready to go. In his first outing of spring, he was touching 98 mph. He’s thrown the 28 hardest pitches of his career working out of the Cubs bullpen, including his first triple-digit fastball against the Dodgers in April. The numbers hardly do it justice; you’ll just have to look at this.
On an extremely related note, Keller, who struck out just under 17% of batters last year, is now striking out 27% of hitters. (He’s part of a Cubs ’pen that went from baseball’s fourth-worst strikeout rate in the first half to third-best in the second half.) In 25 more innings, he’s allowed five fewer homers. That’s in part due to an improved sweeper, which has a 47% whiff rate, one of the five best on that pitch type. But it all comes back to the across-the-board velocity gains, too.
Just over a year ago, Keller couldn’t stick with one of the worst teams in baseball history. Now, on the north side of the same town, he’s headed into October as the closer for one of the better teams in baseball. Let’s never ask why pitchers are chasing velocity ever again.
Gabe Speier, Mariners LHP
Key stat: MLB’s fourth-best K/BB (min. 50 innings)
You want a winding career path? Speier, 30, has been involved in trades that included Yoenis Cespedes, Rick Porcello, Cameron Maybin, Jon Jay, and Dansby Swanson. He’s been dealt four times, designated for assignment once (Kansas City, 2020), and landed with Seattle following the 2022 season when they claimed him after the Royals put him on waivers. (Allowing a 14.51 ERA [!] in 30 Triple-A games will do that.) It hasn’t exactly been smooth sailing there, either; after an OK 2023, Speier missed much of 2024 when a rotator cuff strain around posting a 5.70 ERA and a trip to the Minors.
Healthy again this year, it’s understandable that you might have lost track of him amidst all the talent in the rotation or Muñoz and Matt Brash in the bullpen. With an offseason spent more on training than on rehabbing, Speier found 2 more mph on his fastball – he’s up to 95 now, from last year’s 93 – and his 2.43 Statcast expected ERA, which includes quality of contact and strikeouts/walks, is sixth-best in baseball among qualifiers. It’s worth noting that for the first time, he’s using his four-seamer as his primary pitch, not his sinker. On a rate basis: it’s been the most valuable four-seamer in the game.
Speier’s 33% strikeout rate is in the top 5% of qualifiers, and his 4.8% walk rate is in the bottom 5% of qualifiers, and while there is more to baseball life than just that, it’s an extremely good place to start – especially when one of the only three pitchers with a batter K/BB is some guy named Skubal. While he’s effective against righties, he’s basically unhittable against lefties; he now has two of the best K/BB seasons against lefty batters by any pitcher dating back to 2002.
Jack Dreyer, Dodgers LHP
Key stat: One of just 10 pitchers with multiple pitch types with Run Value of +10 or better
We’ll admit we almost put in Shohei Ohtani here, or Roki Sasaki, or maybe even Clayton Kershaw, and the right answer here is probably “a starter from a high-performing rotation gets moved into relief,” and we like Emmett Sheehan from that group, but if we’re sticking with relievers – and if we’re looking beyond Alex Vesia, a known playoff quantity, with a 1.23 ERA in 19 October games – let’s focus on Dreyer, a 26-year-old rookie whose father Steve was once a teammate of Nolan Ryan with the Rangers.
Like his lefty teammate Vesia, Dreyer has a fastball that features some of baseball’s best “rising” action, ranking seventh on the induced vertical movement leaderboard that Vesia tops. Because of that action, Dreyer’s fastball plays up well beyond its unimpressive 92.7 mph velocity, piling up +11 runs worth of value, which makes it a top-20 fastball in the game. Here’s the trick, though; while Dreyer does have a show-me curve, his other primary pitch is a slider that he’s previously described as “a bad slider” due to its lack of movement.
It is .. not bad. Dreyer’s gyroball slider has allowed only seven extra-base hits all season, and it too ranks highly on the slider leaderboard, currently tied for eighth at +10 runs. That means that Dreyer has two elite pitches, and he’s one of just 10 pitchers with multiple pitch types that have piled up 10 runs or more of value. The other nine are all stars – guys like Crochet, Skubal, deGrom, Skenes.
And also: Jack Dreyer. The guy with the “bad” slider.
Aaron Ashby, Brewers LHP
Key stat: 160 Stuff+ on his slider, best in baseball
We did actually use Ashby last year, but we’re making up the rules here, so let’s do it again. This could maybe be Jacob Misiorowski, but he’s clearly already “too famous” for this exercise, and the Brewers, for all their success, do have some bullpen concerns right now. Nick Mears only just returned from a back injury, and Trevor Megill may not make it back this season at all, and it’s still an open question whether DL Hall can get back in time to contribute. Alongside Jared Koenig and closer Abner Uribe, the best bet here may once again be Ashby, who has spent the last two months striking out around 30% of the batters he’s faced.
It’s not hard to see why. Last year, we talked about how Ashby's velocity had increased, both due to a move from the rotation and due to better health. This year, it’s up even more. This month, it’s up even more than that – Ashby’s 97.8 mph fastballs this month rate as sixth-hardest in the game among lefties.
Paired with a slider that has 7 inches more drop than average – and tops every slider in the sport in Stuff+, which attempts to evaluate pitches based on movement, location, velocity, etc. – and Ashby has allowed just three homers all season long. Now: let’s just hope this goes better than his lone playoff appearance last year. We won’t be highlighting him a third time next year. Probably.
Trey Yesavage, Blue Jays RHP
Key stat: 79% splitter whiff rate in first start
This could just as easily be Brendan Little or Braydon Fisher, really. (Never forget that the Jays got Fisher for merely Cavan Biggio last year, a deal the bullpen-desperate Dodgers surely regret.) Toronto’s bullpen is full of interesting characters ahead of closer Jeff Hoffman. While the Jays haven’t yet made clear their postseason plans for Yesavage, it’s difficult to imagine him cracking the veterans in the rotation to get a postseason start.
But it’s also difficult to see them not wanting to take advantage of the electric skill he showed on Monday, when he struck out nine Rays in his Major League debut, generating immediate comparisons to another righty Blue Jay with an outstanding splitter: Kevin Gausman. Yesavage got 11 misses on 14 splitter swings in his debut, which was merely the third-highest whiff rate in any game this year against a splitter with at least 10 swings, and remember: it was his first game.
In just that lone start, we learned that Yesavage has the highest release point of any pitcher, and the fifth-highest arm angle. We learned that he’s got at least one elite pitch, and a fastball that can touch 96 mph. We don’t yet know how the Jays will use him, whether that’s in multiple-inning stints or higher leverage situations, and this is all extremely unfair to a pitcher who hasn’t yet thrown in his own home stadium yet. (His debut was at George Steinbrenner Field in Tampa, and he’ll throw in Kansas City on Sunday.) But assuming Sunday goes well, the Jays will find a home for him in October. They might have to.
Kyle Hart, Padres LHP
Key stat: Added +2.2 mph to fastball and +9 inches of break to sweeper in relief
Mason Miller very much does not count here, and nor do Robert Suarez, or Adrian Morejon, each All-Stars in the last two seasons. (It’s an extremely good bullpen, even without the injured Jason Adam.) Jeremiah Estrada might, but his second half (4.68 ERA) has been more than a little bumpy. Instead, we’ll dig a little deeper for the lesser-known Hart, who briefly appeared for the 2020 Red Sox before spending the next four seasons in the Minors and Korea. Last year, he won the KBO’s equivalent to the Cy Young award, then signed with the Padres in February.
It didn’t go great, at first. Hart opened the season in the rotation, making six starts with a 6.66 ERA, then spent most of the summer bouncing back and forth between San Diego and Triple-A. Now strictly a reliever, Hart has been lights-out in recent weeks, posting a 13/1 K/BB in September to go with a 2.45 ERA. (And a far more hilarious 0.01 FIP.) Stop us if you’ve heard this before: He’s throwing a lot harder in short relief stints.
Putting numbers to that picture: His four-seamer went from 90.8 mph as a starter to 93 as a reliever, and while that’s hardly “elite,” it’s a lot more acceptable, especially for someone without elite four-seam movement. But, as important: Hart has added a ton of extra movement on his sweeper, which had 8 inches of horizontal break in May and now has 17 inches of break in September. He’s thrown it 41 times this month. He’s yet to allow a hit on it.
Bryan King, Astros LHP
Key stat: 70.8 mph bat speed against, fourth-slowest
No, not Hader. Not Bryan Abreu. We’re talking about the 28-year-old second-year lefty who was taken from the Cubs in the Rule 5 draft back in 2022. The Minor League Rule 5 draft. He’s now made it into 93 games for Houston over the last two seasons, posting a 2.45 ERA, but what’s different this year is that he’s cut his walk rate in half from 2024, and entering Friday he’s on a stretch where he’s allowed exactly one run in his last 17 innings – and he ranks just behind Speier on the K/BB list, striking out more than six for every hitter he walks.
There is, for the most part, not much mystery here. King has learned more on his fastballs as the season has progressed, and since the start of August, he’s allowed a .160 average and .300 average against them, throwing more four-seams and sinkers while generally staying away from his sweeper, which is being thrown barely half as much this month as last. That’s led to a decline in strikeout rate, which is generally not what you’re looking for, but if you’re not walking anyone (97th percentile in walk rate) and not giving up loud contact (93rd percentile in barrel rate) you’re going to get pretty far.
The lack of loud contact is key: while we usually think of bat speed from the hitter’s point of view, it’s also instructive to see which pitchers are focusing batters to slow down their bats the most. Among those with 400 swings against, it’s nice to see that Chris Sale is second, and Vesia shows up in the top 10 as well. King is fourth, and he allows the third-shortest swing length, too – behind Tim Hill and Jhoan Duran. It cannot be a comfortable at-bat, is what this is saying.
Devin Williams, Yankees RHP
Key stat: 44% strikeout rate since Aug. 1, second-best
We’ll finish by breaking our own rules here, because Williams is certainly famous, but he’s also had an extremely up-and-down season, culminating with him losing his closing job to Bednar. Williams’s ERA has jumped from 1.25 to 5.12; he’s allowed five times as many homers as he did last year; he’s had some truly monumental blow-ups in his first (and potentially lone) season in the Bronx that cost him the ninth inning.
And yet: Williams struck out 49% of batters he faced in August. Since Aug. 1, he’s got the highest strikeout rate this side of Mason Miller, and while we certainly won’t put all of his season on “poor luck,” because it’s not, it’s also worth noting that he’s got one of the largest gaps between ERA (5.12) and expected ERA (3.08) in the game. One fascinating reason for that: while Williams has stranded all six runners he’s inherited from pitchers ahead of him, pitchers coming in after him have allowed seven of the 10 runners he’s left on to come on in – runs which have added more than a full extra run to his ERA.
Since a bad game in Houston on Sept. 3, he’s thrown five scoreless outings. While Mark Leiter Jr., Luke Weaver, and Fernando Cruz have all had their struggles lately, the Yankees are essentially forced to rely upon Williams in big spots again. It’s not that hard to see a version of this where the Airbender is bending, and he’s the relief hero we’ve come to know once again.