Article: Kyle Harrison's Tweaks Could Make Him A Key Figure in Red Sox's Rotation Down the Stretch

[Nick John]

When the Red Sox traded Rafael Devers back in mid-June to the San Francisco Giants, the original consensus on the return package was that the Sox got a less-than-ideal haul for their superstar. Returning to Boston was 2024 first-round pick James Tibbs III and three pitchers: Jordan Hicks, Jose Bello and Kyle Harrison. Since then, the trade has still looked underwhelming, as the Red Sox shipped Tibbs to the Dodgers as part of the return for Dustin May at the trade deadline. Bello has been pitching for Single-A Salem, while Hicks has been frustrating to watch with the Red Sox.

Luckily, Harrison appears to have become the most intriguing of them all. especially as he gets more comfortable with the tweaks that the Red Sox have made since he came over from the Giants. While fans thought he might have been in consideration for joining the rotation upon his arrival, the team instead kept him in Triple-A to work on a few things. Harrison, a former Top 100 prospect on lists such as Baseball America and MLB Pipeline, struggled with the Giants this season as he bounced between the bullpen and rotation while appearing in eight games (four starts) and pitching just 23 2/3 innings to a 4.56 ERA before being optioned to Triple-A.  

Justin Willard, the Red Sox's Director of Pitching, feels that the focal point for Harrison will be his fastball, as it averaged 95.1 mph during his short time in the majors in 2025. The team wants to build the arsenal around the fastball and find what could help elevate it.

Two pitches that were a main focus for Harrison to work on were the sinker and cutter, while also changing the grip on his changeup. Prior to coming to the Red Sox, Harrison mainly relied upon three pitches: his fastball, a slurve that at times was confused for a slow, lofty curveball, and a changeup. Despite working on it behind the scenes, Harrison and the Red Sox decided to ditch the sinker after using it just once in his first start with Worcester, instead focusing more on the altered changeup, the new cutter (which at times has been confused for a slider due to its break) and his slurve.

Overall, Harrison is leading with his fastball as was always planned, using it just under 51% of the time (50.9%) while his cutter and slurve are used 18.2% and 19.3% of the time, respectively. His changeup remains his least used offering at 11.7%, though the usage is up from his 9.8% during his time with San Francisco.

When looking at his pitches with the Red Sox compared to his last appearance with the Giants, you can see some noticeable differences. His changeup grip has been altered significantly to alter its spin rate. In his final appearance with the Giants, the changeup had an average spin rate of 2065 rpms; compared to his latest start with the Red Sox, that number fell to an average of 1253 rpms. In effect, his changeup is dropping more as it went from an average induced vertical break of plus two inches in his last appearance with the Giants to now seeing it drop an average of -2 inches with Worcester, while also increasing its horizontal break from 13 inches to 15 inches on average.

The change in his pitches doesn’t end there, with his slurve gaining an average of four inches of horizontal break between his time with the Giants and the Red Sox, again due in part to a change in spin rate (from 2131 rpms on average to 2085 rpms).

The cutter appears to be the most changed pitch, having such a sharp horizontal break (three inches on average in his last start). It seems to be a weapon to challenge right-handed batters in with, being tossed to a left-hander just five times since joining the Red Sox organization. Mainly thrown in the upper-two-thirds of the zone, the small movement helps to make batters late on his fastball.  

The slight tweaks to his pitches have allowed his fastball to play even better now, having generated seven whiffs along with seven called strikes in his last start on August 7. The batters’ timing is off as well, fouling off the pitch 10 times and only managing to put the fastball in play seven times across the start. What might be most promising is the fact that his average exit velocity for his fastball was just 79.2 mph, showing that he is limiting hard contact by mixing his new pitch arsenal around the fastball. This follows a trend of his overall average exit velocity seeing a drop from 92.8 mph with the Giants down to 87.9 mph, along with his hard-hit rate dropping down from 48.5% to 28.3% with Worcester.

With 99 pitches in his last start, Harrison may be closer to being called up than people realize. And with the rotation having two large question marks in May and Walker Buehler, Harrison may be needed to provide some quality innings down the stretch as the team continues to fight for a playoff spot. While the return for Devers may have seemed underwhelming at first, Harrison could change perceptions around the deal in a hurry.

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[moonslav59]

We have Criswell coming off a nice start, Harrison as an option, Fitts probably not as a starter option, right now and the two current starters: Buehler, who did not look too bad, last night and May, who looked good a couple nights ago.

I'm not sure Cora boots Buehler or May from the rotation, so these others may just be pen options for 2025.

[mvp 78]

They are still tweaking his arsenal and I'm not sure he's ready for a callup. 

The WOO numbers don't look very good. His bb/9 is up to 5.23. His k/9 is a career low 9.58. I'd rather they continue to work with him for the remainder of the year and see how he looks in ST. 

[moonslav59]

12 minutes ago, mvp 78 said:

They are still tweaking his arsenal and I'm not sure he's ready for a callup. 

The WOO numbers don't look very good. His bb/9 is up to 5.23. His k/9 is a career low 9.58. I'd rather they continue to work with him for the remainder of the year and see how he looks in ST. 

He had a rough first two starts with Woo (9IP 7 ER,) so if the "tweak" isea is for real, maybe it took a few games to see the results. Here are his game logs since July 9th:

IP ER

3.2 0

6.0 1

3.2 2

5.0 2

5.0 0

5.0 0

Last 3 starts: 15 IP 2 ER (11 hits, but 9 BB. 20 Ks is nice.)

[mvp 78]

15 minutes ago, moonslav59 said:

He had a rough first two starts with Woo (9IP 7 ER,) so if the "tweak" isea is for real, maybe it took a few games to see the results. Here are his game logs since July 9th:

IP ER

3.2 0

6.0 1

3.2 2

5.0 2

5.0 0

5.0 0

Last 3 starts: 15 IP 2 ER (11 hits, but 9 BB. 20 Ks is nice.)

Over that stretch above he gave up 19 bb's. That's a 6.04 bb/9. Who cares about the ERA? You think the hitters a level higher are going to walk LESS? He won't be getting out of those jams against more advanced hitters. You can't simply look at earned runs and say "oh, this guy is definitely ready now." 

[5GoldGlovesOF,75]

Unless Buehler is Kluber bad, he'll be getting a playoff start -- if Boston advances to a best-of-5 series.

The Sox value veteran postseason experience, and are paying Walker good money to repeat what he did last October.

[mvp 78]

8 minutes ago, 5GoldGlovesOF,75 said:

Unless Buehler is Kluber bad, he'll be getting a playoff start -- if Boston advances to a best-of-5 series.

The Sox value veteran postseason experience, and are paying Walker good money to repeat what he did last October.

I think they'd start May over Buehler TBH. Buehler would either go to the pen or be left off the roster. 

Buehler's last 10 starts:

50.1 IP

5.90 ERA

6.71 FIP worst in MLB (SP) over that timeframe

32 BB

55 H

10 HR

1.73 WHIP

1.79 HR/9

5.73 BB/9 (Kyle Harrison-esque) - worst in MLB (SP) over that timeframe

-0.7 fWAR worst in MLB (SP) over that timeframe

[moonslav59]

42 minutes ago, mvp 78 said:

Over that stretch above he gave up 19 bb's. That's a 6.04 bb/9. Who cares about the ERA? You think the hitters a level higher are going to walk LESS? He won't be getting out of those jams against more advanced hitters. You can't simply look at earned runs and say "oh, this guy is definitely ready now." 

The 3 game stretch? It's 9 BBs, which is still ugly as sin.

I'm not for calling up Harrison to start.

I just pointed out he's gotten decent results in his las 3 starts, despite the 9 BBs.

[mvp 78]

29 minutes ago, moonslav59 said:

The 3 game stretch? It's 9 BBs, which is still ugly as sin.

I'm not for calling up Harrison to start.

I just pointed out he's gotten decent results in his las 3 starts, despite the 9 BBs.

The bb's are the bad results. The ERA is luck. It's not a good result IMO. It's clear they are still working on things and he's not able to locate the way he needs to. That bb rate would be unacceptable in MLB. If he has a 6 bb/9 now, it'd probably go to 7 in MLB. That's Darwinzon Hernandez level. Yikes! 

I just think there are other arms down there that they aren't trying to tweak that could get called up instead even just for bullpen help (Tolle, Sandlin, Criswell and maybe even Rule 5 eligible Uberstine/Hoppe). Harrison has a great ceiling, but I want them to take the time to get this tweaking right and make sure his repertoire is fully formed before coming up. That's most likely not going to be until next year. 

[mvp 78]

It's similar to how I feel about Campbell, they are just working on too much stuff with him for a callup to make sense. Let the player get the kinks worked out, find a success and comfort with the new approach, then call them up. When you have a high ceiling guy, it doesn't make sense to throw them back into the fire when you are in the middle of trying to fix them. 

[5GoldGlovesOF,75]

44 minutes ago, mvp 78 said:

I think they'd start May over Buehler TBH. Buehler would either go to the pen or be left off the roster. 

With 40 games left, they could get eight more starts apiece. They probably won't, for all kinds of reasons, but if both Buehler and May continue to be inconsistent, the edge in the playoffs would go to the postseason hero.

I'm not saying I agree with either, since I'm always one to favor talent -- like young Harrison, just a year removed from status as one of baseball's best lefty pitching prospects... but your point about not using an experimental project on a do-or-die stage makes sense (unless they experiment with him all September).

[mvp 78]

Carrasco has similar k/9, FIP, xFIP, xERA to Buehler. I don't believe Buehler has some magical playoff gene that will help him perform. Sox just don't have a viable in house replacement that they believe can replace this DFA worthy arm. 

[moonslav59]

1 hour ago, mvp 78 said:

The bb's are the bad results. The ERA is luck. It's not a good result IMO. It's clear they are still working on things and he's not able to locate the way he needs to. That bb rate would be unacceptable in MLB. If he has a 6 bb/9 now, it'd probably go to 7 in MLB. That's Darwinzon Hernandez level. Yikes! 

I just think there are other arms down there that they aren't trying to tweak that could get called up instead even just for bullpen help (Tolle, Sandlin, Criswell and maybe even Rule 5 eligible Uberstine/Hoppe). Harrison has a great ceiling, but I want them to take the time to get this tweaking right and make sure his repertoire is fully formed before coming up. That's most likely not going to be until next year. 

It's not a great result, but has he improved over his first 2 starts?

[mvp 78]

31 minutes ago, moonslav59 said:

It's not a great result, but has he improved over his first 2 starts?

Sure.

HIs first two starts:

7.88 ERA

3.38 HR/9

[moonslav59]

38 minutes ago, mvp 78 said:

Sure.

HIs first two starts:

7.88 ERA

3.38 HR/9

Well, the conversation was about the Sox making a "tweak" and it improving his production. While improving from horrific to just plain bad might not earn a ML rotation slot, it is still an improvement.

Nobody said 9 BBs in 15 IP was worthy of praise.

[mvp 78]

2 minutes ago, moonslav59 said:

Well, the conversation was about the Sox making a "tweak" and it improving his production. While improving from horrific to just plain bad might not earn a ML rotation slot, it is still an improvement.

Nobody said 9 BBs in 15 IP was worthy of praise.

The tweak is what caused those first two horrific starts. His numbers in AAA for SF were much better than he has shown in WOO. 

[moonslav59]

1 hour ago, mvp 78 said:

The tweak is what caused those first two horrific starts. His numbers in AAA for SF were much better than he has shown in WOO. 

You crack me up, and the funniest part is, you're not even trying to.