12 under-the-radar relievers who could dominate October

You remember the relief heroes of last postseason, right? No, we're not talking about Craig Kimbrel or Aroldis Chapman. We are of course referring to household names Kevin Ginkel and Josh Sborz. What about the year before, when it was Nick Martinez, among others -- or in 2021, when the Braves rode Tyler Matzek and friends to a title?

You get the idea. Each October, some lesser-known reliever gets hot at the right time, and it changes the shape of a short series. Sometimes, it changes the outcome of the entire season.

Who, then, might that pitcher be this year?

It’s too easy to say that you might see great things from playoff-bound relievers such as Josh Hader or Emmanuel Clase, because of course you will -- they’re elite. You might say that Matt Strahm or Jeff Hoffman aren’t nationally known -- yet they were All-Stars this year. But what about the names you really don’t know that well yet? Who, six weeks from now, will be The Next Kevin Ginkel, a title that is worthy of a whole lot more respect than one might think?

There are so many relievers. There are so many choices. Among the teams most likely to reach the playoffs -- sorry, Tigers, and all of your suddenly interesting options -- here are our dozen favorites, in no particular order. (All stats are through Sunday's games.)

Luke Weaver, Yankees RHP
Key stat: MLB's largest K% increase from 2023-’24.

You’ve probably heard that Yankees fans are not exactly full of confidence in Clay Holmes, and Deadline acquisition Mark Leiter Jr. hasn’t been able to keep the ball in the park. So then, their October bullpen star, if there is one, might end up being ... a 30-year-old journeyman who has been on five teams in the last three seasons, and entered this year with a 5.14 career ERA. Sure, why not.

The 2024 version of Weaver is a very different one from the guy who was cut loose by both Seattle and Cincinnati last summer. As a Yankee, Weaver ditched his slider and curve and then increased his usage of his cutter, but more importantly than that, he's turned his four-seam fastball into an elite pitch seemingly out of nowhere. Check out the differences in Weaver’s heater, and you’ll see where the success is coming from.

• 2023 // 94 MPH // 16 inches rise [IVB] // 88 Stuff+
• 2024 // 95.7 MPH // 18.4 inches rise // 140 Stuff+

What do all those numbers mean? Basically, he’s throwing it harder, and doing it with more of that all-valuable vertical break pitchers are going for, and that the advanced models think the quality of the pitch went from mediocre to one of baseball’s best fastballs. Easy, right? (It is not easy; it required changes to his grip and delivery.)

Last year, Weaver struck out 19% of hitters. This year, it’s 29%. It’s the largest increase in baseball.

Lucas Erceg, Royals RHP
Key stat: 25/2 K/BB w/KC

Erceg isn’t a secret to prospect experts who spent years watching the former second-round pick try unsuccessfully to hit his way through the Milwaukee system as a third baseman, all while being open about his off-field struggles, before finally converting to the mound in 2021. He reached the Majors last year on the strength of his 98 mph fastball and showed promise, but he struggled to throw strikes. This year, he managed to improve the walk rate some (down from 14% to 7% with Oakland) before being traded in July. And then?

Erceg has pitched in 19 games for the Royals. He’s walked all of two hitters, whiffing 25, in large part because his first-pitch strike rate has leapt from 56% to 67%. That’s at least partially fueled by Kansas City getting him to focus on his high-velocity fastballs a little less, and a little more on his surprisingly good slider -- which he’s now using one-third of the time, or more than twice as often as he did with Oakland last season.

Unsurprisingly, his chase rate has jumped from poor (5th percentile) to excellent (80th percentile), because hitters can’t sit on the fastball -- thanks to what has been, on a rate basis, one of the most valuable sliders in the game. It's not just about the fastball for the strong-armed former infielder.

Kaleb Ort, Astros RHP
Key stat: 1.41 ERA since joining HOU org.

Ort, 32, had a 6.19 ERA in parts of the last three seasons with Boston, then found himself a frequent flyer – at least on paper. Last winter, he was passed around the waiver circuit by Seattle, Miami, Philadelphia and Baltimore before the season began. He'd ultimately find himself posting a 12.08 ERA (really) in a dozen games for the Orioles' Triple-A affiliate before the organization put him on waivers yet again in late May.

Claimed by the Astros, Ort then only allowed two runs in 16 Triple-A games, joined the big club, and has allowed just four runs in 18 games for Houston. What that means is that since leaving that 12.08 ERA in Norfolk, Ort has a 1.41 ERA in 38 1/3 combined innings in the Astros organization. He looks like a different pitcher, and that’s because he is a different pitcher. But what’s changed?

It’s easy -- so easy -- to simply look at this fastball velocity chart, note that he’s added 2 MPH since last year (he now touches 100) and move on. It’s helped to be sure, but Ort was also averaging nearly 97 mph in Triple-A this year, too, and obviously that didn’t work out that well -- so it's not just that.

Instead, the real difference is in a new pitch, namely his cutter, which he introduced briefly last year and now represents 21% of his pitches.

Ort told the Houston Chronicle last month that he’d always planned for the cutter to be a large part of his offerings this year, but a spring knee injury limited him, and he never threw it more than six times in a game for Norfolk. In his very first game for Houston affiliate Sugar Land, he threw it nine times. Two games later, it was 10 cutters. So far, he’s allowed just two hits off it in the bigs, and though it’s not a strikeout pitch -- his cutter has yielded just one K -- it helps keep pressure off his high-velo four-seamer.

A.J. Puk, D-backs LHP
Key stat: 32/4 K/BB w/ AZ

Puk was the sixth overall pick in the 2016 Draft, so he’s not exactly an unknown, but he struggled to stay healthy or productive with Oakland and Miami, where he began the year with four hard-to-watch starts (9.22 ERA) in an ill-fated attempt to convert back to the rotation that ended when he was sidelined with shoulder fatigue.

Returning to the bullpen in May, he was quite good in 28 games out of the Miami bullpen (2.08 ERA / 2.45 FIP), and then he’s been fantastic in 21 games for Arizona since being traded at the Deadline (0.43 ERA / 0.74 FIP), with strikeouts exploding and walks disappearing.

• w MIA: 24% K / 12% BB
• w AZ: 45% K / 5% BB

It’s not, however, about throwing more pitches in the zone. It’s about the pitches he’s throwing just being unhittable. Puk, when he was trying to be a starter, was throwing six different pitches. But by the time he was traded to Arizona, the sweeper, splitter, and changeup were gone, and since joining the D-Backs, he’s all but eliminated his sinker as well.

It's worked: His swinging strike rate has nearly doubled, from 11% with Miami to 21% with Arizona, as his chase rate has jumped from 29% to 39%.

Michael Kopech, Dodgers RHP
Key stat: 2 runs allowed in 19 games w/ LAD

You saw what he did on Sunday night in Atlanta, right? No?

Like Puk, Kopech is a former top pick (first round, Boston, 2014) who has been involved in a high-profile trade or two and has had some difficulties finding consistency around injuries and moves between the rotation and the bullpen. Like Puk, Kopech was traded from a last-place team to an NL West contender this summer, and, again like Puk, the performance since has been game-changing.

After a 4.74 ERA in 43 games of relief for the White Sox, Kopech has posted a 0.95 ERA in 19 games for the Dodgers. He’s not that good – no one lasts forever allowing zero home runs – but interestingly, this isn’t really about a massive change in approach. While it initially seemed he’d throw his four-seamer less, he’s now back up to exactly the same 79% he was using it with Chicago.

Instead, the main change seems to be: Don’t throw strikes? As a Dodger, his first-pitch strike rate has dropped from 66% to 52%, and his zone rate has gone from 54% to 44%. It’s maybe not the most expected approach, but it’s working so far.

Kris Bubic, Royals LHP
Key stat: 7.75 K/BB ratio

Stop us if you’ve heard this story before: Young pitcher struggles for years trying to stick in the rotation, then goes to the bullpen, simplifies his repertoire and/or ups his velocity, and finds success. That would describe Bubic, who had a 4.85 ERA in parts of four seasons (2020-’23) primarily as a starter before undergoing Tommy John surgery early last season. When healthy this summer, he returned as a reliever, primarily because that’s where Kansas City needed the help.

Based on the returns so far, it’s fair to wonder if he’s ever going back. Bubic’s 3.33 ERA doesn’t stand out, but the 2.18 FIP absolutely does, and 31 K's to four walks is stellar. As you'd expect from a now-healthy pitcher working in short stints out of the bullpen, the velocity is way up, from 91.7 to 93.2 MPH on his fastball, and a changeup that is now 5 MPH faster than it was three years ago. But it's this, too. It's the shelving of the curveball that didn't work, and the addition of a slider that plays better.

Two years ago, Bubic's fastball was one of baseball's least valuable pitches, allowing -20 runs worth of value thanks to a .348/.587 BA/SLG combination. So far this year, he’s nearly doubled the swing-and-miss rate on it.

Justin Martinez, D-Backs RHP
Key stat: 100.2 MPH average on sinker

Last year, Martinez averaged 100.6 MPH on his four-seamer, but still managed to allow 14 runs in 10 innings, and he was not included on Arizona's roster for either the club's 2023 postseason run or for Opening Day 2024. Martinez still throws 100, of course, but now he’s got a 2.43 ERA and he’s become one of the primary ninth-inning options for Torey Lovullo as Paul Sewald attempts to overcome inconsistency.

What’s changed? The kind of fastball he’s throwing. Last year, his primary fastball was a four-seamer, which had elite velocity but was relatively straight. This year, he added a sinker, which still goes 100 MPH, but does so with nearly 8 inches more drop and 4 inches more break than the four-seamer did. Call it whatever you want, but the takeaway is this: What if you could add a ton more movement without sacrificing velocity? You’d want to do that, right? To his credit, that’s exactly what Martinez was able to do.

"It was my idea,” he told Jack Sommers in May. “I noticed that when I would throw my fastball I wasn't really drawing any soft contact. I wasn't getting any double play balls. So I decided to implement the sinker. "

While Martinez’s most valuable pitch was and is his splitter, which has allowed only six hits (five singles) all season long, it’s the change in fastballs that’s been key. In last year’s cameo, his four-seamer allowed a .731 slugging percentage. This year, the sinker has allowed a mere .390 mark – in large part because, as intended, it’s considerably more of a ground ball pitch.

Cade Smith, Guardians RHP
Key stat: +27 runs on 4-seamer, MLB’s most valuable pitch

This is a tough line to walk, because the Cleveland bullpen has been so excellent all season – it’s the primary reason for their success – that it’s difficult to claim any of their top arms are “out of nowhere." At the same time, it’s unreasonable to make a list like this about potential October breakout relievers and not include someone aside from Clase, too. So, with all due respect to Hunter Gaddis and Tim Herrin (and, believe it or not, new call-up Andrew Walters), we choose Smith, who has spent all season having the kind of year that would garner him Rookie of the Year support if not for an extremely deep pool of AL candidates.

Smith, 25, went from a Canadian high school to the University of Hawaii, then was an undrafted free agent signing in 2020 (when the Draft was only five rounds). He piled up strikeouts in the Minors, yet was limited by an inability to control walks. That hasn’t quite been a problem in the bigs, because as nice as that 2.00 ERA looks, we’re more impressed by the 98/17 K/BB – so much for walks being an issue – and a fastball that is currently rated as The Most Valuable Pitch In Baseball. Really.

It’s a lot more than you’d expect from a fastball that is thrown at a good-not-elite 96 MPH and without any obviously notable movement or shape. Instead, it appears to be about deception – about a Hader-esque ability for a tall man with a low release point to absolutely confound hitters. It doesn’t hurt, to be sure, to have it paired with a splitter that absolutely falls off the table.

Aaron Ashby, Brewers LHP
Key stat: 31% K-rate as RP

Milwaukee’s bullpen has been a huge part of its success this year; only Cleveland’s relievers have a lower ERA. Maybe this should be Trevor Megill, though we predicted he'd have a great year; it might have been breakout lefty Bryan Hudson, before last-summer struggles landed him back in Triple-A. No one’s noticed how good Joe Ross has been since moving to the ‘pen, either, allowing just one run in 20.1 innings.

But watch out for long-time prospect Ashby, who was a swingman in 2021-’22 before shoulder surgery cost him all of 2023. Back in the Minors for most of this season, another attempt to start went quite badly – an 8.36 ERA in 16 starts – and he was eventually shifted to the bullpen, which is where he remained when Milwaukee recalled him in late August. To say it’s gone well is an understatement, even with a poor outing on Sunday against Arizona. In seven games and 13.1 innings, Ashby has allowed a .160/.192/.220 line against, striking out 16 against only two walks.

He is, as you’d expect, throwing harder in short stints. A lot harder.

How hard? Ashby's 97.1 MPH in September is the sixth-hardest four-seamer/sinker velocity among lefties in the game.

Keegan Akin, Orioles LHP
Key stat: Career-high 31% K-rate

Akin is sort of like Ashby: A lefty swingman type who has been in his current organization for years while battling injuries and inconsistency. As recently as six weeks ago, Akin was optioned to Triple-A, and at the time he was having a perfectly fine yet unremarkable middle relief season, posting a 3.34 ERA in 56.2 mostly low-leverage innings. When he returned, his first two outings were poor, but look what’s happened over the last month: 10 games, 20/1 K/BB, a line of .146/.159/.268 against. That’s including Tyler O’Neill’s walk-off homer last week.

It’s tempting to write this off as a small sample, and it is. On the other hand, Akin’s season-long expected ERA is in the 96th percentile, well beyond anything he’s done before. He’s added considerable hop to his four-seamer, going from decent rise to strong rise. What he’s done most recently, however, is something else. He’s used his slider far more than he ever had before, a career-high 40% of the time this month. His fastball is up a full MPH from what it was before his brief demotion. It’s possible that this “new” Akin is just a hot run, because he’s been around for a while. But there’s some real under-the-hood changes, too.

Griffin Jax, Twins RHP
Key stat: K-rate increase from 25% to 33%

This is maybe unfair, because after a failed attempt to stick as a starter in 2021 – a 6.37 ERA in 18 games, mostly starts – Jax has been a pretty solid reliever in each of the last two seasons for Minnesota, including four scoreless innings in last year’s postseason. But he’s hardly nationally known, and this year he’s taken his game to an entirely new level, posting the fourth-largest increase in strikeout rate among pitchers with 50 innings in both seasons.

What’s different now is just that everything is more. His fastball velo is up to a career-best 97.1 MPH; his first-pitch strike rate is up to a career-best 70%; his swing-and-miss rate is up from 27% to 37%; his changeup, which at 92.3 MPH is faster than a lot of fastballs, is dropping more than an extra inch from last year. Jax, the previous two seasons, was good. Jax, this year, is great.

Jeremiah Estrada, Padres RHP
Key stat: 99th percentile fastball rise

As with the Guardians, there’s not exactly a shortage of high-quality San Diego relievers to choose from here – watch out for rookie Sean Reynolds, who has 21 strikeouts in his first 11 innings – and if you think this should be Jason Adam and his 0.43 ERA, so be it. But Adam has been a high-quality reliever for three seasons now, and Robert Suarez and Tanner Scott are probably too famous, so we’re going with a pitcher who was cut loose by the Cubs less than one year ago.

Estrada, to be fair, is a little famous himself, having struck out 13 consecutive hitters at one point this season, and his success isn’t really hard to explain, because it’s a very 2024 approach to pitching. Step 1: throw a fastball very hard with elite rising action. Estrada throws 97 with top-of-the-scale rise. Step 2: throw a splitter with a weird custom name. Estrada’s brand-new split-change hybrid plays off his fastball quite well. He calls it a “chitter.”

There’s some small concern about the rising walk rate as the season has gone on. He's also allowed one hit this month. He’ll be a real weapon in October.