Why Couldn’t Orion Kerkering Dominate With The Sweeper in 2025?
Major league managers determine their bullpen trust trees fluidly throughout the regular season. Pitchers in the best rhythm earn high-leverage innings in October. While the Philadelphia Phillies have fortified a…
Major league managers determine their bullpen trust trees fluidly throughout the regular season. Pitchers in the best rhythm earn high-leverage innings in October. While the Philadelphia Phillies have fortified a bullpen that’s looked dangerously thin at certain points in 2025, they’re staring at one disappointing hole they probably didn’t expect.
Would Rob Thomson feel comfortable calling on Orion Kerkering during Red October? The 24-year-old righty allowed a run in four consecutive September outings. He allowed 10 earned runs in only 20⅓ innings after the acquisition of Duran, and he struggled to handle his intended role inheriting and stranding runners in the "dirty inning" in middle relief.
Kerkering's impressive 2.29 ERA in 2024 ballooned to 3.30 ERA in 69 games in 2025. David Robertson has unquestionably jumped him as the primary right-handed set-up man in the bridge to closer Jhoan Duran.
The Phillies will turn to Kerkering in the middle innings during the playoffs with sparing options behind him, especially among the right-handers.
However, the fading intimidation of his once dominant putaway pitch has knocked him down the pecking order in a bullpen gearing up for a World Series run.
Sweeper/Slider
Orion Kerkering burst onto the scene in September 2023 with a dominant sweeper, a pitch that synergizes the vertical break or a curveball and the horizontal break of a slider.
He became a darling of the organization’s focus on analytics and the “Stuff+” metric emphasized by biomechanics expert Dan Aucoin.
The pitch morphed this season, and its characteristics push observers to refer to it as a slider, slurve, breaking pitch, or any of the other interchangeable new-age names that irritate Ricky Bottalico in his pitching breakdowns.
Kerkering leaned on the nasty pitch heavily in 2024 with a 56% usage rate. Hitters whiffed at 31.2% of his sweepers. However, he dialed back the usage to 48% in 2025. Opponents made significantly better contact with a 23.6% whiff rate only narrowly above the 22% major league average.
Thomson commented on Kerkering’s struggles on Sept. 23 after an extra innings loss when the young righty allowed the ghost runner to score and an additional earned run in the 10th inning.
“Not a whole lot of swing and miss right now. Execution is basically what it comes down to. The stuff’s good – he was 98-99. Probably execution of the slider is where it’s (the problem is) at.”
-Rob Thomson
What’s Wrong With Orion Kerkering?
Kerkering’s poorly-timed slump sparked a conversation between Ricky Bottalico and Jayson Stark on Unfiltered during Stark’s weekly Wednesday appearance.
“That sweeper of his when he first got to the big leagues was a devastating pitch. It was like a flubber ball. 40% swing and miss rate. This year, that’s down to a 22.7% swing and miss rate. They obviously still think that’s his best pitch… He throws it more than any other, but it’s caused him a lot of problems.”
Stark had previously spoken earlier this season on 97.5 The Fanatic about the morphing sweeper after Orion Kerkering finished April 2025 with a 5.56 ERA. He cited major league scouts who suspected that hitters have an easier time picking up the pitch at Kerkering's release point.
Bottalico offered a theory about a pitcher with a limited three-pitch arsenal. Kerkering depends on the velocity of his fastball and sinker, which usually sit in the 96-97 mile per hour range, as the complementary pitches to the sweeper. How could a pitcher of his style attempt to offset his lack of a changeup?
“I know when he first came up, it (the sweeper) was more like a slider. It was a late-breaking slider. Now, they’ve changed it to the ‘sweeper,’ which is kind of an in-between pitch. I think – and I’m guessing why they did this – is that he doesn’t really have an offspeed pitch. They probably tried to slow it up a little bit, so players have to back up, speed up, slow down.”
Kerkering’s velocity with the sweeper has remained relatively even in the 86 mile per hour range. However, StatCast tracks the pitch’s movement in 2025 with more vertical break with a curveball style and less horizontal break with a slider style. The numbers have shifted from his first full major league season in 2024.
Bottalico is also skeptical of Kerkering’s ability to command his fastball with confidence, and Thomson has openly encouraged his right-hander to attack the zone more aggressively with his fastball.
Rebound Entering MLB Playoffs
Kerkering snapped a streak of four consecutive outings with an earned run during a scoreless appearance on Saturday. He entered the game with two outs in the seventh inning and a man on second. He struck out Royce Lewis, the only hitter he faced, chasing a sweeper.
“It was good. He went right after the hitter. We wanted to get him in an inning where there's traffic out there, and he got out of it. That was good.”
-Rob Thomson
He earned the victory on Sunday with a scoreless 10th inning, stranding the ghost runner with another opportunity to pitch with men on base. He struck out the side, getting James Outman and Austin Martin to chase sweepers out of the zone and freezing Ryan Jeffers on a called strike three with a sweeper at the bottom of the zone.
Thomson spoke optimistically about the final two outings building Kerkering's confidence entering the postseason.
The Phillies, however, will enter the MLB Playoffs with questions unanswered about a homegrown pitcher they hoped could become a backend stud sooner rather than later.
All stats courtesy of StatCast, Baseball Reference, and FanGraphs.
