Jacob deGrom is, famously, hyper-attentive to his mechanics. It's part of what makes him great.
No pitcher is more on top of his own delivery. That's why, when deGrom is at his most dominant, every pitch looks like a carbon copy of the last.
If the smallest link of the chain is out of whack, deGrom feels it -- let alone something big like a change in his arm slot.
And that's exactly what's happening in 2025: deGrom's arm angle this season, his first full one back from his second Tommy John surgery, is significantly lower than in years past.
The 36-year-old's average arm angle this season is 30 degrees -- his lowest in the five years of Statcast arm angle tracking. (A zero degree arm angle would be perfectly sidearm, and 90 degrees would be straight over-the-top.)
The Rangers ace, of course, is attuned to the difference. It started as a natural shift to the arm slot that felt most comfortable as he returned from surgery, and it became a conscious part of his mechanics as deGrom learned to pitch with a lower release.
"When [my arm angle] climbs," deGrom said at Yankee Stadium this week, raising his pitching hand in the air to demonstrate a slightly higher release, "I noticed I got a little bit more sore. So I was just trying to do what's best for health. And now I feel like with the slot that I'm at right now, I've been able to recover really well in between. So it kind of naturally happened, and a little bit on my own. It's a little bit of both."
As deGrom has adjusted to his arm slot, he's steamrolling hitters like vintage deGrom again. In his last three starts, deGrom has recorded his first 10-strikeout game of the season, shut out the Astros for eight innings, and locked down the Yankees lineup with seven innings of two-run, nine-strikeout baseball.
The 2025 version of deGrom might have a new arm angle, but he's starting to look like his old self.
Visually, the difference between Mets deGrom and Rangers deGrom is minute. But it's measurable in the data.
Statcast's arm angle tracking only goes back to 2020, so we don't have deGrom's arm slot from his back-to-back Cy Young seasons with the Mets in 2018 and '19. But we do know what it was in 2020 and '21, when he was also dominating. deGrom's arm angle in 2020 was 35 degrees; in 2021, it was 36 degrees.
So deGrom's arm slot has dropped down at least five degrees between then and now. That's a real change.
And the shift is consistent across deGrom's arsenal.
DeGrom's arm angle change by pitch type, 2020-21 vs. 2025
- 4-seamer: 34 degrees to 28 degrees
- Slider: 37 degrees to 32 degrees
- Changeup: 37 degrees to 31 degrees
- Curveball: 40 degrees to 36 degrees
DeGrom's four-seamer and slider -- maybe the most overpowering pitch combo in baseball -- are the ones that necessitate the most care from deGrom when it comes to his mechanics.
That's because a lower arm angle -- closer to sidearm, even ever so slightly -- makes deGrom's pitches more likely to pick up horizontal movement. Which he doesn't want out of his four-seamer and slider.
deGrom wants his heater to ride through the zone and his slider to snap straight down underneath it. He wants to keep the movement tight, and north-south. That's how he can pound the glove-side edge of the strike zone so relentlessly and consistently.
Such a movement profile is easier to maintain with a higher arm angle, which can make commanding his two biggest weapons simpler.
"Sometimes I'll get a little beside [the baseball] and run it a little more, which I don't like," deGrom said. "But I'm still making adjustments."
So when deGrom first returned to the Rangers at the end of last season, he forced his arm slot a little bit higher than the one he's been pitching out of this season. deGrom averaged a 34 degree arm angle down the stretch in 2024, which is still lower than the 37 degrees he was averaging in his 2023 Rangers debut before he got hurt, but not as low as where he's sitting in 2025.
But an offseason of work and a Spring Training of testing his arsenal with the lower arm angle has allowed deGrom to adapt successfully.
"I think last year I was actually probably a little bit higher still," deGrom said. "But then this year, throwing, I was like, 'OK, well, that feels really good.' So I was kind of just going based on feel there. And then you've got to see in spring how the stuff plays."
This isn't the first time deGrom has returned from an arm injury with a lower arm slot. After right elbow and shoulder injuries forced him to miss the end of 2021 and the start of 2022, deGrom came back down the stretch for the Mets' '22 playoff push with a 32 degree arm angle, compared to the 36 degrees he was at in '21. But by the start of 2023 when he joined the Rangers, deGrom's arm angle was back up to its old slot.
So deGrom's arm angle might tick back up if he regains the right feel for it. There have been signs of that lately. His arm slot has been slightly higher in May, averaging 31 or 32 degrees in three of his four starts this month, after being under 30 degrees in four of six starts in April.
"It's a little bit higher [lately]," deGrom said after his start against the Yankees. "So it's constantly adjusting and just seeing what works best."