Kyle Harrison Is a Different Pitcher in Boston Than He Was in San Francisco

Kyle Harrison is morphing into a different pitcher than the one the Red Sox acquired from the Giants as part of June’s jaw-dropping Rafael Devers deal. That was the plan when Boston brought him on board, as evidenced by the 24-year-old southpaw’s having spent close to three months in Triple-A following the swap. With 182 2/3 big league innings under his belt, the former top-rated prospect in the San Francisco system was sent to Worcester to have his repertoire reconfigured.

His primary weapons remain largely the same. Harrison still attacks hitters with a one-two combo that Eric Longenhagen called “an uphill fastball” and “a big bending breaking ball.” The former is an 94.8-mph heater, while the latter is an 84.2-mph offering that is categorized as a slurve.

And then there are the new additions.

“First and foremost, there is the cutter,” said Harrison, who has made two appearances and allowed one run over nine innings since making his Red Sox debut on September 10. “There is also a sinker that I can mix in to lefties. I have a new changeup grip, as well. Everything else is the same. The four-seam is kind of how I’ve always been identified — and I still have the slurve — so now it’s been about adding the other secondary stuff to protect it.”

Harrison mentioned adding a cutter when I spoke to him early last season, but the pitch never really took hold. Per Baseball Savant, he threw only six of them in 2024. As for the changeup, there have been multiple iterations. After tweaking his original grip last year, he is now a member of the kick change generation.

“It used to be similar to Logan Webb’s changeup — the way he throws his with a one-seam orientation — but I’ve switched to a kick,” Harrison explained. “That’s what I’m trying to harness. It is a little harder to get a feel for. Throwing a kick kind of takes away that being perfect, of trying to pronate a pitch and get to a spot. Now it’s, ‘Throw the pitch and let the kick take care of it.’”

The early results are promising, particularly in terms of movement profile.

“With the old changeup, I was usually positive vert — positive-one, positive-two, and then negative-two at best,” said Harrison, who has thrown 46 kick changes (8.8%) since his call-up. “I’m consistently negative now, so this pitch could definitely be an eye-opener for me. I love how it’s feeling so far; it’s just a matter of getting more comfortable with it. I need to consistently get it over the plate, and I also need to be able to command it out of the zone. When I was in Triple-A, I was leaving some of them over the middle of the plate.”

Leaving his original organization — the Giants took him in the third round of the 2020 draft out of Concord, California’s De La Salle High School — spurred the change.

“I never really tried any new changeup grips over there,” Harrison told me. “Then I got here to Boston. We tried one down in Worcester that was some form of a splitter, but it didn’t really have the best shape, so we tried the kick change. That’s when I started to clip some negative-fives, negative-eights. That’s when it was like, ‘All right, we can throw this thing.’ Again, we just need to get it over the plate.”

Throwing his slurve to both sides of the plate is yet another post-San Francisco adjustment. Whereas his old club mostly wanted the pitch arm side, away to righties, Red Sox pitching coach Andrew Bailey has talked to the lefty about having more of a back-foot approach.

“With the Giants, I felt like I was boxed into just going backdoor to righties with it,” Harrison said. “Here, it’s cool that they want me to throw that thing under bats. I think that’s the next step for that pitch — trying to get some chase. If I’m getting ahead with my other stuff, I can use it to get swings, especially against aggressive teams.”

That Harrison’s arsenal and approach are undergoing adjustments is in many ways not a surprise. His San Francisco tenure, which spanned parts of three seasons, included a 4.48 ERA and a 4.56 FIP over those aforementioned 182 2/3 innings. By and large, he was falling short of what had been high expectations.

What is somewhat surprising is that, even though the Giants are generally regarded as a savvy pitching organization, it took a change of scenery for the adjustments to happen. I asked Harrison for his thoughts on that being the case.

“I guess I’d say that I’m not surprised,” Harrison said. “I was kind of their top prospect, so it was almost like me just getting by with my stuff. They didn’t want to change me, in a sense. When I got over here, it was kind of cool to step into kind of a developmental phase where I could experiment with new pitches and see what I liked. I could feel the good ones, feel the bad ones, and go from there. Now I’ve got five pitches. I’m definitely happy for this opportunity.”

And why wouldn’t he be? He is scheduled to start tonight at home against the Tigers. His team’s magic number is one. Just a few months after San Francisco shipped him up to Boston, Harrison has a chance to be the winning pitcher in a game at Fenway that sends the Red Sox to the postseason. Some opportunity, indeed.