Thomas White is one of the game’s top pitching prospects. Drafted 35th overall in 2023 by the Miami Marlins out of an Andover, Massachusetts high school, the 21-year-old southpaw is ranked ninth on our newly-released 2026 Top 100 Prospects list as a 60-FV prospect. Moreover, only two pitchers rank in front of him, neither of whom throws left-handed.
The 6-foot-5, 240-pound hurler has grown as a pitcher since he was first featured here at FanGraphs in an August 2024 Sunday Notes column. Which isn’t to say he hadn’t already been making a name for himself. White, who was taking the mound for the High-A Beloit Sky Carp when I first spoke with him, ranked as Miami’s no. 4 prospect that summer, with Eric Longenhagen citing both his mid-90s fastball and plus slider when assigning him a 45+ FV. Our lead prospect analyst did include a caveat in that writeup: “He has impact starter upside and carries with him the risks typical of a volatile teenage pitching prospect.”
A year-and-a-half later, White is coming off of a 2025 season during which he dominated hitters to the tune of a 2.31 ERA, a 2.27 FIP, and an eye-opening 38.6% strikeout rate across three levels. He finished the year with the Triple-A Jacksonville, and while he is expected to return there to start the upcoming campaign, he shouldn’t be a Jumbo Shrimp for long. Possessing one of the highest ceilings among his prospect contemporaries, White is on the doorstep of the big leagues.
White discussed the continued development of his arsenal, and the mechanical tweaks he’s recently made to his delivery, in a recent phone conversation.
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David Laurila: We first talked before a game at West Michigan, when you were playing in the Midwest League. Outside of being 18 months older and presumably 18 months smarter, has anything changed for you as a pitcher?
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Thomas White: “I mean, there has been a lot of mechanical stuff and a little bit of approach. Other than that, nothing revolutionary, I would say.”
Laurila: Can you address the mechanical changes?
White: “I took some changes into the 2025 season, but those were relatively [minor]. The big changes I’ve worked on have mostly been this offseason. I’ve kind of gotten back closer to how I naturally throw. I’ve gotten my stride to be almost a foot longer. I’ve gained back a lot of extension I used to have. I’ve gotten back to my lower three-quarters slot, high extension, a lot of carry.
“Again, I wouldn’t say they were revolutionary changes, but I’m getting back closer to how I naturally throw. If you were looking at video from when I was 15 [years old], and then from last year, it’s so different. It’s kind of crazy. This year, it’s about trying to get somewhere in between all the stuff that I learned through high school and into my pro career, kind of mated together with what I naturally do pretty well.”
Laurila: How did you get away from what you do naturally?
White: “Once you get into pro ball, there become a lot of cooks in the kitchen. Sometimes that can mess with some guys. Going into the 2025 season, I was working on getting into my back leg a little bit better, and I think I overcooked it a little bit. I almost started doing it too much. I created this almost Darvish-like coil that shortened my stride. The arm timing was later. The front side was pulling out a little bit. My extension dropped a good bit. I also had back issues toward the end of the season, especially my last six starts, I would say.
“There was a lot of east-movement and not a lot of north-south, so I really just worked a lot on direction and timing stuff, getting my momentum moving toward the plate. It started to naturally come back and blend itself into what I ended the offseason at.”
Laurila: Where is your extension now, and where was it last season?
White: “When I got drafted, it was probably around 6-6, and last season I’m pretty sure it was like 6-foot or 6-2. On TrackMan — this might not be the most accurate thing — I’ve gotten to 7-foot-1 so far this past offseason. I’m averaging about 6-7, 6-8. I’m feeling a lot better there, staying behind the ball a lot better.”
Laurila: I recall you telling me in West Michigan that you were in the process of gaining a better understanding of pitch metrics. How much have you grown in that area?
White: “I wouldn’t say I’m a TrackMan warrior or anything, but I’ve grown to know how to use one, and how each metric affects my pitches. I wouldn’t say that I could design a pitch based off of TrackMan, but I know that my fastball carries better if I can keep the tilt at 11:15. If it’s 10:45, that means my arm is probably a little bit late and the ball is going to have a little more run to it. If I can get that tilt to 11:00 or 11:15, I’m going to get 18, 19, 20 vert, which is what I’m looking for.”
Laurila: Are you chasing… that may be too strong a word. Are you trying to achieve certain metrics on your pitches?
White: “Like you said, chase is a bit of a strong word. But there are some goals. My fastball plays better at the top of the zone, and obviously more vert plays better at the top of the zone. Those metrics, along with my pitching style and how I throw, play well. And they play well off the rest of my arsenal. So the more vert the better, but I’m not going to say I’m chasing a specific crazy number.
“It will help, too, that my release height is a little bit lower than it was last year. Even if the vert is kind of the same, it will still look like a little bit more because of the lower slot.”
Laurila: Can you elaborate on your arm slot?
White: “My delivery height was all over the place last year. At some points it was 6-3; at some points it was 5-7. I ended the year probably around 6-foot, maybe 6-1. Right now I’m averaging around 5-8, 5-9.”
Laurila: Is there a sweet spot that you and pitching staff have determined?
White: “It’s somewhere between where I am now and 6-foot, which is the highest I would want to go. Once I get above that, the carry gets really good on my fastball, but the rest of my pitches suffer from it.”
Laurila: Your sweeper slider is something else we talked about at West Michigan. How has that progressed?
White: “It’s gone through a couple of iterations. I have a new grip for it as of last year. It’s had some inconsistencies, but toward the end of the year, I really started to figure it out. It moves relatively the same — maybe with a little more horizontal — but the big thing is that I’m throwing it a lot harder. I’ve been up to 87. My goal had been to average 83-84 mph. When we last talked, it averaged maybe 80.
“The velo is the more important part. In terms of the horizontal, it kind of depends on the day. If I’m really feeling it, it will be hard and have some good horizontal. I would say the worst — the bad days now — are pretty similar to what it was in High-A. I don’t know exactly what I’ve been averaging, although the biggest one has been 22. The average isn’t close to that.
“The sweet spot… mine has always been a little bit slurvy, so the sweet spot might be around 16 horizontal. If it’s 16 horizontal and I can throw it 84-85, I feel really good about that movement. I don’t think I need to be Joe Ryan with a 30-inch sweeper.”
Laurila: What about the vertical? You mentioned slurvy, but are you trying to be around the zero line?
White: “I had some points last year where it was close to that. The goal at the beginning of the season was to get it close to the zero, but I personally have experience with this — some of the metrics have backed it up a little, too — and it’s a little better when it actually has a little bit of depth to it, a little two-plane. So, my goal is probably -5, -6.”
Laurila: Are you still throwing a gyro slider?
White: “Yeah, I still have that. I’ve been running into some issues with it not being as hard as I’d like it be. The movement is where I want it, it’s just that I would like to have it be 88-90, and right now it’s 86-87. Being a pronator, sometimes I have a bit of a hard time getting the velo on it. It’s a work in progress in terms of that.”
Laurila: You were throwing a two-seam changeup when we talked last. Has anything changed there?
White: “I still have a two-seam grip, but I throw the kick-change now. When I was in High-A, it was more of a run pitch — I relied more on it running off the plate than on depth — and we’ve changed the philosophy to get depth on the pitch, and not worry about how much it runs.”
Laurila: Marlins pitching coach Daniel Moskos described the organization’s pitching philosophy to me as “throw nasty strikes,” with an emphasis on attacking the middle of the zone and letting your stuff play. Is that basically your approach?
White: “Pretty much. They’ve been hammering that, especially to the guys who walk more people than everybody would like. Yeah, that’s basically what they’ve been preaching.”
Laurila: How would you grade your command?
White: “I don’t think my command is too bad. I tend to have innings, or batters, where I lose it, but then it comes right back. My problem is that sometimes I tend to mess around with hitters instead of just putting them away by just throwing it right in the zone. I just need that consistency. If I’m ahead of guys, I have to just put them away and not try to get too cute with it.”
Laurila: Any closing thoughts?
White: “There were a lot of changes last year. The surface numbers were good, but overall, I don’t think it was as good of a season for me as maybe the numbers would suggest. I try to hold myself to a pretty high standard. I made a lot of changes — some of them good, a lot of them probably not so good — so I was excited to get into the lab this offseason. My player plan was consistency. I had a lot of really good pitches last year — I clipped a lot of really good stuff — it’s just that my consistency and my ability to repeat it wasn’t where I wanted it to be, or where the org wanted it to be. So it was, what can I do to find those consistent movement types that make my pitches as good as they can be?”