Spencer Arrighetti has been featured twice here on FanGraphs as an independent, yours truly interviewed the Houston Astros right-hander in April and August of his 2024 rookie season. On both occasions, he displayed an impressive knowledge of pitching analytics, as well as a thoughtful approach to his craft.
Our third conversation ended up focusing on his curveball. Arrighetti has been throwing at a 31.4% clip this season, and not only has it been his most used offering, it’s been the most successful. As of this writing, it has yielded a .121 batting average and .151 slugging percentage while achieving a whopping 50.9% whiff rate. Arrighetti, who took the mound just seven times last season because of a broken thumb and right elbow swelling, has started five games this year to a 4-1 record and 1.88 ERA over 28 2/3 innings. I talked to him about his turn at Fenway Park earlier this month.
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David Laurila: He’s throwing a lot more curveballs than he has in years. Why is that?
Spencer Arrighetti: “Before I got hurt, it was a top-10 curveball in baseball. That makes me feel confident to throw it to anybody, at any time in the equation. Having a pitch like that goes a long way, especially as a starting pitcher. I’ve just leaned on it a little bit more this year. In the past, I’ve had a thought process that to get a catch or a bunt – it’s hard for you to ride the ball quickly. position – to make the hitter early on it, or be out of position and get that there are guys I can send it to as often as I want, on the spot, off the spot, and get good results.
“My velocity is also down a little bit this year, and that’s another reason I’m running away from fastballs at certain points – even though I think I threw 35%, or maybe 40% fastballs the other night against the Yankees. I felt good about it, really good command of the top train. Two pitches play from left, up and up, up and up. and then you throw. a sweeping curveball from it, it’s a tough tunnel to follow.
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“The results speak for themselves. Obviously I don’t want to do anything, because I’m going to continue to throw my curveball a lot. But yeah, the increased usage is a confidence thing, and understanding that when I play it, it’s one of the best pitches in major league baseball.”
Laurila: Was throwing more curveballs a plan coming into the season, or was the high usage natural?
Arrighetti: “It’s a living thing, honestly. The last few years I’ve tried not to make my game plan so much based on stats, but rather on something that works. Right now, every time I throw a pitch, it’s the one I believe in the most. I can sleep well at night if it’s hit on the phone in a big game.
“That’s something I didn’t do in my rookie season. I tried to get the middle ground, and that’s why I threw something. Now I throw what I believe in the most. My belief in that pitch is higher than before, which makes me move on it, or just drive it. I believe that will bring a good result.”
Laurila: Is it always the same curveball, or do you manipulate it to get different shapes and speeds?
Arrighetti: “I’d use it a little bit. There are some hitters where speed is the reason they’re going to have better or worse results. I’d throw it a little bit where I know a guy is struggling with pitches that are under a certain speed limit, because their swing is going fast, or they’re having trouble slowing it down, slowing it down to reload and swing.
“It’s funny to talk about it in a vacuum, because it doesn’t really happen in a vacuum in baseball – the context is, ‘How did I get to this number?’ where he knows that speed will be the difference, and not necessarily stopping. A lot of times, that comes down to being able to throw good fastballs in the zone, as I was saying a little bit earlier. But I can say that fraud, for me, is very slow, understanding when I can take it slow, knowing that the results will be good. The same can be said for throwing it hard. I will add a more sharp movement, as opposed to a big movement. They all have their time and place for the right guy.”
Laurila: Sequencing and setting up platforms is important…
Arrighetti: “Yeah. That goes back to the fastball. You’ve got to give him a reason to try to get the foot down early and the swing. I think my average curveball velocity this year is probably somewhere around 76 [mph]and the heater is about 92-94 in diameter. The velocity gap is big enough that… I can’t really put a quantitative number on it, but I firmly believe that, on average, they are fast enough to get to where the ball is out of the hitting zone by the time the barrel gets there. That is a very good thing.”
Laurila: Can you see yourself throwing more curveballs than fastballs during the season?
Arrighetti: “No, I don’t think that’s sustainable at all. Not from a results standpoint, but more so from a standpoint of continuing to feel good. The curveball is a high-stress pitch, especially if I’m trying to throw it hard. That’s another reason I lean toward being fair because it’s slower, it feels better on the shoulder. It’s sustainable that way.
“My rookie year, the average velocity of my curveball was probably two or three miles per hour up, because I was trying to throw it as hard as I could all the time. I’ve come to understand that that’s not necessary at all. If anything, it’s the limiting factor in my ability to throw it a lot.
“I think I’ll always mix it up, but again, I don’t think I’ll ever throw more curveballs than fastballs. If I were a reliever, I think it would be easy to do that. In a small sample, I’ll throw the one that I believe in the most, and that I believe is the best analytical result, more often than not. But as a fastball starter, being able to throw the fastball three times.”
Laurila: Apparently he had an elbow problem last year, although it didn’t require surgery.
Arrighetti: “I had a sprain in my UCL, and I look at that because of the mechanical adjustments I made to try to throw harder, more so than to raise the use of spin. The proof of that would be, this year my mechanics feel very similar to where they were in 2024. I can throw a lot of curveballs without pain. I can throw a lot of distance without pain. It’s a goal-related thing Knowing when to step on the gas, and knowing when I don’t need to, go It’s really long and I don’t have a problem with my elbow.
Laurila: Your curveball is definitely back after missing some time.
Arrighetti: “I didn’t throw 16 weeks during the year. I usually throw all year long. I don’t really go out at the end of the season, because I feel like that’s kind of a straight ticket to losing the feel of certain things, especially catching certain things, or just your mechanics in general. But as soon as my mechanics felt right again, the spin came back.
“With pitchers who have surgery, you get distracted when it comes to spinning the ball, because you feel that maybe that’s how you got hurt in the first place. [that] it wasn’t like that for me. Again, I’m not really mentioning the pain in my elbow from spinning the ball. That’s something that always comes easily to me, not something that would hurt my elbow.”
