Justin Dunn, Justin Grimm, and Tyler Mahle on the Cultivation of Their Curveballs

Pitchers learn and develop different pitches, and they do so at varying stages of their lives. It might be a curveball in high school, a cutter in college, or a changeup in A-ball. Sometimes the addition or refinement is a natural progression — graduating from Pitching 101 to advanced course work — and often it’s a matter of necessity. In order to get hitters out as the quality of competition improves, a pitcher needs to optimize his repertoire.

In this installment of the series, we’ll hear from three pitchers — Justin Dunn, Justin Grimm, and Tyler Mahle — on how they learned and developed their curveballs.


Justin Dunn, Seattle Mariners

“I had a curveball before I had my slider. I learned it from my dad at 12 years old. He used to play in men’s leagues, and while he never played at a real high level, he loves the game. He’s a student of the game.

“Essentially, I take a two-seam grip and put my thumb underneath, finger through the lace, pressure to the ball.When I was younger, he would tell me to just throw it like a football, to never turn my wrist down. It would be big, loopy, and slow. As I got older, I started to throw harder and understand finger dexterity and about pulling the ball down. I learned that I could pull a little bit more with my middle finger and get it a little tighter, and sharper.

Justin Dunn’s curveball grip.

“It’s a big command pitch for me. I use it to get ahead, and I’m never afraid to double it up. Because I’ve been throwing it for so long, I’m confident that I can land it when I want to. So yeah, I’ve had a curveball since I was 12 years old. I learned the slider when I was 16. My buddy Keven Pimentel and I were at a tryout, playing catch, and he threw one to me. I was like, ‘That was sick. How did you throw it?’ He showed me, I threw one right back to him, and he was like, ‘Bro, how did you do that?’ I said, ‘I don’t know. I just did what you told me to do.’

“My curveball and slider tend to blend. My curveball will be seen as a slider sometimes, because they’re very similar in shape. My curveball is more of a slurve. They have the same shape. They have the same action. The curveball is just a little slower, a little bit bigger and loopier. And I command it a little bit better.

“I command my curveball better because the thought process is ‘strike.’ I’m trying to throw it for a strike, whereas I’m aggressive with my slider. I’m trying to throw it through you. I’m trying to rip it, to get that short, tight break. Not that I don’t throw my curveball with conviction. It’s just that I’m not necessarily setting my sights down. I don’t care if it pops up. If it pops up, and the hitter sees it pop up… I honestly want that, because more times than not they’ll see it and be like, ‘That looks different.’ And then it’s in there for a strike. Now I have multiple options, because I can play with it and make it tighter. I can make it come out a little flatter. I can make it come out loopy when I want to. So again, it’s not that I don’t throw my curveball with conviction. It’s just that I feel more confident about getting it in the zone.”

Justin Grimm, Milwaukee Brewers

“I was throwing a curveball at 12 years old. When I was in Little League, the high school pitching coach showed me a grip. The one thing he said is, ‘Make sure you get on top of this pitch, and throw it like a fastball. That’s what you want to think.’ So that’s kind of how it came about. The older I got, the more I understood how to throw it and what I was feeling.

“So I learned it at a young age, but I don’t recommend that. After all these studies they’ve shown… young kids throwing curveballs just isn’t a good idea, because not every young kid understands. They’re going to want to turn their wrist. When I threw mine at a young age, I kept my wrist straight and tight, but instead of throwing a fastball, I threw a curveball.

Justin Grimm’s curveball grip.

“Here and there, it was good and bad over the course of the next decade. When I got into pro ball is when I really started ripping through it and having that mindset, instead of just aiming it. It became harder and got more depth. And while I tinkered with a few grips, I always ended up going back to the one I first learned. It’s a very standard curveball grip, something a 12-year-old kid can learn. It’s a pitch I don’t think a lot about. For the most part, it comes naturally to me.

“I have worked on tunneling it better. That’s something that’s come up over the last few years — tunneling my curveball to make it play best off my heater. It’s something I continue to work on. Of course, I’m working on a lot of things.

“I think the difference between a curveball that pops out of your hand is… that goes back to aiming it versus just throwing it, and trusting it. You’re picking out a visual spot. You pick out a spot, and throw your curveball with the intent that you’re going to throw it through that spot. That’s how you drop it in the zone without having it pop out. When it starts popping out is when you’re behind in the count and are like, ‘Oh, I’ve got to get this over for a strike.’ That mindset changes the way you throw the pitch. Of course, it can depend on your arm angle and the way you naturally deliver a pitch. For some guys it naturally doesn’t pop out, while other guys have to really work on that effect.”

Tyler Mahle, Cincinnati Reds

“I began throwing one when I first started playing baseball… or when I first started pitching, I guess. As soon as I was throwing off a mound in games, I was throwing a curveball. That probably would have been in Pinto [League]. My dad taught me how to hold it, and then I threw it. It was probably just a loopy whatever, but I was only seven or eight years old.

“But I didn’t really learn to throw one until… shoot, probably not until a couple of years ago. Or even last year. I mean, I was throwing a curveball, but it wasn’t a good one. To throw it the right way and get the… you know, once you get the Rapsodo, and get the spin you want… how to make it more efficient, and all that stuff. Technically, I haven’t thrown a really good curveball yet.

Tyler Mahle’s curveball grip.

“I changed the grip last year, and then I changed it again this past offseason. I found a grip that’s more comfortable. I guess I’d explain it as going down the horseshoe, as opposed to up the horseshoe. It helps when I’m superconscious of how my whole hand and forearm are. If you ask Trevor Bauer, he says to keep it super neutral, and not [pronate or supinate]. So I grip it, and when I throw it, the best thing is to keep my arm neutral — my wrist up to my hand. That’s helped me a lot. But it’s still a work in progress.

“I would like for my curveball to be an out pitch. For now it’s not, because I can’t get it big enough to where it looks good out of my hand then gets under the zone and bounces in the dirt. I need more vertical break. If I could give you the answer to why I can’t, I would go out and throw it.

“I did [throw a lot of curveballs] last year, and that got me in a lot of trouble. I gave up a lot of runs on that pitch — especially with two strikes. I would try to throw it under the zone, but I would end up leaving it over the plate. Most of the time that was hit over the fence. I mean, the break just wasn’t good. I think I averaged seven or eight [inches] vertical break, which is terrible. That’s why I adopted my slider. It’s a little more tilted than a normal slider, but I can throw that one under the zone better. My curveball — an actual good curveball — again, it’s still a work in progress.”


The 2019 installments of this series can be found here.

David Laurila grew up in Michigan's Upper Peninsula and now writes about baseball from his home in Cambridge, Mass. He authored the Prospectus Q&A series at Baseball Prospectus from December 2006-May 2011 before being claimed off waivers by FanGraphs. He can be followed on Twitter @DavidLaurilaQA.

newest oldest most voted

I love these pieces.