Casey Mize Added a Second Slider That Isn’t a Sweeper (At Least Not Yet)

Casey Mize had seven big league appearances under his belt when he was featured here at FanGraphs in January 2021. He also had high expectations. Drafted first overall by the Detroit Tigers out of Auburn University three years prior, the right-hander ranked 32nd when our 2021 Top 100 Prospects list was published that February. Bullish on his ability, Eric Longenhagen projected Mize as a “no. 2 starter capable of pitching at the top of a contender’s rotation.”

Our lead prospect analyst’s assessment came with an “if he stays healthy” caveat. Longenhagen wrote that he was “sufficiently scared of Mize’s injury history… to slide him behind players of a similar talent.” Those concerns have unfortunately been validated. The 28-year-old hurler required Tommy John surgery in June 2022, and he has also landed on the shelf with a handful of comparably mild maladies.

His numbers reflect the time missed, and the impact that it has had on his career. Entering the current campaign, Mize had thrown just 291 innings as a Tiger, and his ledger included a lowly 9-19 won-lost record to go with a 4.36 ERA — not exactly what was expected from a high-profile draft pick with a high-ceiling arm.

Tigers fans are finally seeing the Casey Mize they’ve been yearning for. On the heels of a more middling return-from-surgery 2024 season, the resurgent righty has gone 12-4 with a 3.68 ERA and a 3.98 FIP over 22 starts comprising 117 1/2 innings. Pitching behind Cy Young favorite Tarik Skubal, Mize has nearly matched rotation mate Jack Flaherty in the WAR department, and in four fewer starts.

A visit to Driveline over the offseason has helped fuel Mize’s success. Displeased with last year’s performance — his 4.49 ERA and 17.3% strikeout rate stood out like sore thumbs — he traveled to the training facility just five days after the season ended. What resulted were tweaks to how he grips and releases the baseball.

“I flipped the seam orientation on my four-seamer, so it’s carrying a little bit more,” Mize explained. “I’m tracking down with the seams instead of up. That’s something they told me I could benefit from. They also wanted me to add a slider that actually went left. So, I’m throwing a bigger slider now. I don’t call it sweeper, because it only goes like eight inches to the left. It’s not getting the correct seam orientation to move more than that, partly because I’m throwing the patch of the ball.”

Asked if he meant that he is spiking his pointer finger off of a seam, the righty answered in the affirmative.

“Yeah, with a baby spike,” he told me. “Again, I can’t get the seam orientation right to where it’s super seam-shift on the seam, but I’ll work on that at some point. It’s not what I was trying to do, so I can definitely maximize it more. I am getting some good results with it, though.”

The sweepier offering is an addition to Mize’s repertoire, as opposed to a replacement. His Baseball Savant breakdown reflects as much. Savant shows Mize having thrown a total 466 sliders last year (as well as 15 pitches that were categorized as slurves); this season, they have him throwing 266 sliders and 280 slurves.

His original slider has a somewhat different movement profile than it did a year ago.

“It was a little gyro slider, and I’m still throwing it, but now that I have the one that goes left, [the gyro] has actually kicked up,” said Mize. “Whereas in the past it was like zero and three — just like a real gyro — now it has a little more of a cutter characteristic to it.”

Pitchers tweaking their repertoires at outside facilities over the offseason is common in today’s game, and in Mize’s case it occurred even though he’s in an organization that excels at pitch development. According to the hurler, the Tigers had no issue with his doing so.

“It was basically, ‘Here is my plan,’” Mize told me. “We were in contact about that. It was, ‘This is what they recommend; what do you guys think?’ The Tigers told me what they thought and we took both ends of it. We worked together. I think everybody is on board with me getting better.”

Mize has clearly been better this season, but that doesn’t mean he sees himself as a finished product. Far from. A case in point is his stated desire to add more horizontal to his slider/slurve. Outside of that, what is he most wanting to improve going forward?

“The horizontal [on the slider] is probably the biggest thing on the docket,” Mize said to my question. “Ideally, I’d like to have better sinker characteristics than what I’m currently doing. It’s not a sinker, it’s a two-seam fastball. It’s funny to me that they want to call every two-seam fastball a sinker, while we seem to have eight different names for sliders. But yeah, I’d like to cut a little bit of vert out of the two-seamer. I don’t want to throw a two-seamer and look up and see [positive] 15 vert. I want to see 11. It’s a minuscule change, but I don’t want to carry it near what I’m carrying my four-seamer at. Having pitches that carry differently is a good thing. That’s me nit-picking a little bit, but every little bit [of improvement] helps.”