Spencer Schwellenbach, Casey Mize and DL Hall on their paths as young MLB starters (2024)

There isn’t a single starting pitcher under 25 who is qualified for the ERA title this season. As far as baseball has advanced in the science of what makes a pitch good in a vacuum, this fact still stands as a testament as to how hard it is to become an established young starter capable of a full season in the big leagues.

Being healthy and having good pitches theoretically has to give way to fitting all the pieces together in a way that works. And that takes time, and that process is often interrupted by injury. So when you look at the ages of this trio of pitchers, you might find they are a little older than you expected. It’s just hard to be great right away.

These are their stories about the process of taking that raw clay and molding it into the vision of success they see in front of them.

Spencer Schwellenbach, Atlanta Braves

A 24-year-old who pitched only sporadically before converting from position play in his junior year at Nebraska, Schwellenbach is in the process of breaking out at just the right time for the Braves’ needy rotation. That’s not the most common story, but it did lead to a unique fastball that is part of the righty’s foundation. Why is it unique?

“Having a low release,” he said last month. “The release point is not common. I played shortstop, I’ve always thrown the ball from down here.”

But there are plenty of pitchers who throw from lower angles. Schwellenbach has to put in work to make sure his fastball doesn’t look like the typical one from his arm slot.

“The more you go down there, the less vertical you’re going to get, the more flatter you’re going to get,” he said of the four-seamer. “I’ve been trying to cut spin, so it doesn’t tail. The more it tails, the less flat it’s going to be.”

In this visualization by Max Bay, you can see that cutting the tail (and getting closer to zero horizontal movement) makes Schwellenbach’s fastball better by making it less normal and therefore more deceptive. The heart of the ovals depicted is the most “expected” movement from a given arm slot. Aaron Civale throws from a similar release point but his movement is much closer to expected. Schwellenbach, by cutting his fastball a little, remains out of the heart of the circle with his four-seam movement.

The work left for him to break out is refining the cutter, curve and split-change that he also throws. The difference between his fastball and cutter is just a tucked thumb, a subtle difference that nevertheless affords him 2-plus inches of drop and cut off the fastball. He recently changed his curve grip to a spike that has given him a couple of ticks of velo and a couple of more inches of drop.

“The pitch was more of a get-me-over-for-a-strike five weeks ago and now I can throw it for a strike but also finish it,” he said of the curve before modeling his grips for me.

Apologies for the awful camera work, but you can still see how tonight’s Braves starter Spencer Schwellenbach changed his fastball grip to kill horizontal movement and make it stranger (and tougher for hitters) with respect to his arm slot. Bonus is his curve grip change. pic.twitter.com/VmwqGFGO0b
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— Eno Sarris (@enosarris) August 16, 2024

The curve has been working so well recently that he’s sporting four above-average pitches by Stuff+, paired with above-average command. That might be enough to make him an even better pitcher next year, but if he ever dials in the splitter as well as he’s done with the curve this year, the sky’s the limit. Right now, he doesn’t practice the change between starts and just sees if he’s got it during the games.

“Whatever’s working that day, I just kind of go with it,” he said.

And it’s all working pretty well.

Casey Mize, Detroit Tigers

Drafted first in 2018, Mize has transformed while with Detroit.

“My delivery is a little different but nothing crazy,” the 27-year-old said this month. “I had back surgery, which has changed some functional stuff. Now I am more upright and vertical, and that’s come over in the fastball.”

Fixing the back was huge because he had nerve pain in his left side, which for him is the “blocking” leg — the leg that comes down in front and provides the ground force reaction that helps convert a pitcher’s rotational energy into velocity that’s directed at the plate. Studies of the blocking leg’s impact into the ground have shown it to be highly predictive of velocity. Mize got the surgery and found some ticks in his fastball as a result.

“After the surgery, I was in a position where I could get over my front side and carry the ball at the top of the zone,” he said. “It was posture-based. I have less nerve pain, I wasn’t even able to stick my front leg in the ground and get over my front side, but now I can do that a little better.”

Maybe you can see that here — a slighter taller stance through release on the right, this year. Look at the angle of his shirt hitting his belt.

While he was getting right physically, Mize was changing his arsenal. Most notably, he left the sinker behind in favor of a four-seam.

“Got away from the two-seamers to lefties because that was getting crushed in ’20 and ’21, so more four-seamers to those guys,” he said. “I’ve had a lot more success against lefties than righties this year, so it’s been a more complete arsenal to lefties.”

So why has Mize been good against lefties (.399 slugging) and struggled against same-handed hitters (.476 slugging)?

DL Hall, Milwaukee Brewers

Staying healthy has been the biggest struggle for Hall, who came to the Brewers from Baltimore in the Corbin Burnes trade. The 25-year-old lefty has dealt with knee, back and elbow issues that derailed him. But, like with Mize, getting those things right allowed him to be more upright and may end up helping him in the long run.

“I changed a lot mechanically because of my back and elbow injuries,” Hall said this week. “I was too rotational, now I’m more directional. When I had the low back problems last year, I wasn’t able to get any thoracic extension, and I was pulling my shoulders forward and getting rotational so I didn’t get into my back. I had to get it healthy. Stand tall, keep my shoulders back, and then I’ll get into the right positions.”

While he was working on getting the knee healthy, it turned out he had to get his ankles healthier, too. As a runner, I’ve struggled with my ankles collapsing inward, or pronating, and Hall said that was an issue for him, too, until he’d found some exercises to help.

“I have the exact same thing in my ankle!” he exclaimed. “I do a lot of stuff to strengthen it. Trying to tighten the ankle — do a little toe yoga. It’s huge. Sit down, have your leg at 90 and then move them around like this.”

Of course there’s a video, replete with the customary soft yoga soundtrack.

Once the toe yoga and knee and back and elbow rehabs had their desired effect, Hall was freed up to think about the actual specifics of his pitches. He’d originally gained a plus changeup when he first got to pro ball and discovered that his curveball grip didn’t work on a ball that had lower seams. But even that changeup has gotten better over time.

“I changed my grip on that changeup for the first time,” he said of the pitch. “I’ve always thrown a two-seam circle like that and then I changed it to like a four-seam. I found that my middle finger was working more than my ring finger, so with that old grip, that middle finger was getting too much of the ball, so I would get ride on it. Now with this grip it’s getting more sideways spin. I threw it four years and it was really good, but now it’s more consistent.”

DL. Hall shows his changeup grips before (left) and after (right). (Eno Sarris / The Athletic)

With the new grip, he’s got the best drop and fade on the pitch that he’s ever had, and the numbers agree that it’s been more consistent. In the meantime, he’s re-found his curveball, which he’s now throwing 80-plus mph with more drop and cut than the average fastball. That looks like a real weapon. The last stop, just like Mize, might be the slider, which has shown inconsistent horizontal movement over the past few years.

“In ’21 I had an elbow injury, so I came back in ’22 switched to a sweeper so I didn’t have to torque so much, I was letting the grip do it,” he said of the slider. “It made it a lot bigger and lefties were able to recognize it. I knew that my goal was a tighter, harder slider, but I was trying to find a happy medium. I went back to the bullet last year, but I still used the sweeper a lot. It was way too slow, though. Lefties didn’t swing at it and I couldn’t bury it back-foot to righties. This year, I am throwing the bullet, I just didn’t have the arm speed to get it fast again.”

The good news is that the slider is consistently regaining velocity throughout this season. The better news is that, as a lefty, he has the weapons he needs to get righties out without it. The best news is that he’s feeling good in the back, elbow, knee and ankle. That makes him poised to regain his promise, help the Brewers in October and end up again on sleeper lists going into next season.

(Top photo of Spencer Schwellenbach: Alex Slitz / Getty Images)

Eno Sarris is a senior writer covering baseball analytics at The Athletic. Eno has written for FanGraphs, ESPN, Fox, MLB.com, SB Nation and others. Submit mailbag questions to esarris@theathletic.com. Follow Eno on Twitter @enosarris