Behind Kyle Harrison’s Breakout | Brew Crew Ball

It’s June 5, roughly two-and-a-half months into the baseball season. The current ERA leaderboard (and Cy Young Award shortlist) is:

As tempting as it would be to turn this into another Jacob Misiorowski article, we’ve already covered his dominance at length. Instead, let’s compare those three pitchers to Brewers’ No. 2 starter Kyle Harrison:

Kyle Harrison (MIL): 1.57 ERA, 1.029 WHIP, 2.7 WAR, 11 GS, 7-1 record, 57 1/3 IP

Harrison hasn’t quite thrown enough innings to qualify, but his ERA would rank second in baseball — behind only Sánchez. He’s already been worth almost three full wins above replacement (WAR), comparable to Misiorowski and Schlittler, and has a lower WHIP than Sánchez. It’s not exactly hyperbolic to say that through his first 11 starts as a Brewer, Kyle Harrison has been one of the best pitchers in baseball.

A little over three months ago, when the Brewers traded for Harrison, I wrote an article explaining why Brewers fans should be more excited about him. He was once a top prospect, highly regarded enough to be the main piece in a trade for Rafael Devers, but his development had stalled out a bit in major league stints with the Giants and Red Sox.

Knowing the Brewers would likely overhaul his arsenal — as they often do with young, developing pitchers — that article was my attempt to predict how they might mold Harrison into a more effective starter. Now that he has enough innings under his belt for a meaningful evaluation, we can look back at that article and see how close it came to what the Brewers actually did. In the process, we’ll examine the adjustments that have helped fuel Harrison’s breakout season.

Harrison’s arsenal has always been anchored by his late-rising fastball — the best pitch in his arsenal — but for most of his career, his main secondary options (changeup and slurve) were somewhat lacking. Looking back, the first article did a pretty good job of identifying the adjustments he needed to make:

“What does Harrison need to live up to his potential? Simply put, he needs better shape on his secondary pitches and a go-to secondary offering.”

As it turns out, those two improvements are exactly what fueled his breakout.

In 2024, Harrison threw a changeup 19.8% of the time. Opposing batters weren’t particularly fazed by that iteration, hitting .287 with an xSLG (expected slugging percentage) of .461. This year, opponents are hitting .292 against the pitch, but with an xSLG of only .385. While his changeup hasn’t exactly become Airbender-esque, he’s limiting hard contact and forcing hitters to respect it.

Much has been made of Harrison adopting a new changeup grip, the “kick change,” from former Giants teammate Hayden Birdsong. Birdsong’s changeup is notable for its unusually low spin rates, often registering in the 1,200 rpm (rotations per minute) range. Harrison’s changeup in 2024 averaged 1,946 rpm. This year, it’s all the way down to 1,233 rpm.

Changeups with lower spin rates usually drop more as they reach the plate. Implementing the kick change has fundamentally changed the shape of Harrison’s changeup:

2024: 16.4” tail (horizontal movement), 1.0” rise (vertical movement)

2026: 11.4” tail, 3.7” drop

His changeup actually breaks less overall than it did in 2024, yet it’s been more effective because its shape complements the rest of his arsenal. Every fastball-oriented pitcher can benefit from an effective changeup, as the two pitches are typically thrown from a similar arm slot with comparable arm speed and release points. Harrison’s best pitch is his rising fastball, and the changeup plays off it beautifully. Thrown from the same arm slot and with a similar release to his fastball, his changeup arrives slower and breaks down instead of up, making it much more difficult for hitters to square him up.

The other reason Harrison’s changeup has been more effective? He’s throwing it less often. In 2024, he threw the pitch 19.8% of the time. This year, that figure is down to just 10%.

That might sound counterintuitive, but not every pitch benefits from being featured heavily. Harrison’s changeup is a useful complementary offering, yet it’s clearly his third-best pitch. By reducing its usage, he’s able to lean more heavily on his fastball and slurve while still keeping hitters honest.

That said, there is a point where a pitcher can become too predictable. Harrison has thrown just 11 changeups over his last two starts, good for only 5.5% of his total pitches. The changeup’s value doesn’t come from being a wipeout pitch; it comes from forcing hitters to respect a third option. If hitters stop expecting it altogether, some of that value disappears.

One of the things Harrison was reportedly working on in his time with the Red Sox was developing a higher-velocity version of his slurve, which had potential but wasn’t consistently effective. Opponents had an xSLG of .471 against the pitch in 2024 and .518 in 2025.

In the February article, I mentioned that Harrison was throwing his slurve nearly two mph faster in 2025 and getting an extra 1.6” of vertical break. Previous articles on Harrison had noted that a slightly harder breaking ball might be the answer, which I brought up as something that the Brewers could “have already pinpointed.” It looks like they have:

2024: 80.6 mph, 8.7” break, 4.6” drop

2026: 82.1 mph, 10.9” break, 3.8” drop

As you can see, with the increase in velocity has come a change in shape. Harrison’s slurve has 2.2 more inches of horizontal break while dropping almost an inch less. This year, opponents have hit .115 with a .222 xSLG in 64 plate appearances against the slurve. In 2024, before he’d started implementing the new version, opponents hit .274 with a .471 xSLG.

Harrison is throwing the slurve more than he ever has (29.2% of pitches), and with better results. He’s not getting more spin on the ball, or more extension, but that small increase in velocity has given it a much more effective shape and turned it into what looks like a true go-to secondary offering.

Because his secondary pitches historically haven’t been that effective, and because it’s his best pitch, Harrison has always thrown his fastball a lot — like, almost 60% of the time. His fastball’s best quality is its shape rather than its velocity, but when velocity declines, so does movement. Lower velocity also gives hitters more time to recognize the pitch and square it up.

With all that said, it’s not a surprise that his success has been pretty directly correlated to his fastball velocity:

2023: 93.6 mph, 4.15 ERA, 1.154 WHIP, 7.5 hits/9, 9.1 K/9

2024: 92.5 mph, 4.56 ERA, 1.343 WHIP, 9 hits/9 , 8.5 K/9

2025: 94.6 mph, 4.04 ERA, 1.374 WHIP, 8.8 hits/9, 9.6 K/9

2026: 95.0 mph, 1.57 ERA, 1.029 WHIP, 6.8 hits/9, 11.5 K/9

His best season in terms of fastball velocity has also been his best overall season so far, his second-best velocity year was his second-best overall season, etc. You get the idea.

Unlike his changeup and slurve, Harrison hasn’t significantly altered his fastball or its usage rate. Instead, the pitch has benefited from two developments: increased velocity and a stronger supporting cast. Hitters have less time to react, and they’re less able to gear up for the fastball because Harrison’s secondary pitches now demand respect.

Another big change, one that I didn’t predict, is Harrison’s positioning on the rubber. He used to pitch from the third-base side, but this year he’s been working from the first-base side. The adjustment gave him a different angle of attack against hitters and changed the way each of his pitches played, especially the slurve.

As explained in this great breakdown, Harrison’s slurve breaks away from left-handed hitters, so moving to the first-base side of the rubber allows him to release it from a more deceptive angle. The pitch appears closer to the hitter out of his hand, making it more difficult to track and judge whether it will finish in or out of the strike zone. Against right-handed hitters, the slurve starts farther outside, increasing the likelihood that hitters either give up on it too early or recognize too late that it’s going to clip the zone.

The final change, and another that I didn’t bring up in the first article, is Harrison’s arm angle. Harrison raised his arm angle from a low three-quarters arm slot to more of a true three-quarters release. His release point, as you can see below, also moved further toward first base.

While Harrison’s new arm slot accentuates the benefits of moving to the first-base side of the rubber, it also comes with advantages of its own. A higher release point allows pitchers to get more on top of the baseball, which can increase spin. Harrison’s fastball spin rate has jumped from 2,203 rpm in 2024 to 2,359 rpm in 2026, and he’s getting about three more inches of vertical break.

The other piece of the puzzle is his vertical approach angle (VAA). Milwaukee has long favored pitchers with flatter VAAs because they create a deceptive effect, making fastballs appear quicker and causing hitters to swing underneath them.

Harrison has historically had a very flat VAA because of his lower arm slot, and because it accentuates the effect of his rising fastball. In order to keep the advantages of a flat VAA without losing the benefits of a higher arm slot, Harrison — as Matthew Trueblood detailed here — has introduced mechanical adjustments, getting lower into his delivery before release to keep his pitches flatter.

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When you dive into the tweaks Kyle Harrison has made this year, it’s no surprise that he’s turned into one of the best pitchers in baseball. The talent was always there. Harrison always had the raw ingredients to become a solid major league starter; he just needed better secondary pitches and a few mechanical adjustments that maximized his strengths.

Now, he has both. His revamped arsenal and refined delivery have transformed him from a pitcher with intriguing upside into one who is beginning to realize it. If these changes continue to hold, Harrison’s ceiling looks much higher than “solid.”