The Brewers Have Done It Again With Kyle Harrison

The number of success stories to come through the Brewers’ pitching lab in recent years is quite remarkable.

Year after year, the Milwaukee Brewers target arms with untapped potential or take on reclamation projects in an effort to help pitchers realize their true ability. Last year, Quinn Priester, whom the Brewers acquired from the Boston Red Sox at the onset of the 2025 season, was the perfect example of this.

This year, Kyle Harrison has the makings of being Milwaukee’s next success story. After acquiring the 24-year-old southpaw from the Red Sox this offseason, Harrison has emerged as an essential member of Milwaukee’s rotation after his first few turns through.

A highly-touted prospect coming through the Giants’ system, Harrison has bounced around to a couple of organizations after failing to settle in at the big-league level to this point. But his most recent clubhouse change may have unlocked a level that his previous organizations could not achieve.

While it’s too soon to draw any sweeping conclusions, it appears the Brewers’ pitching development has done it again.

A Bumpy Path To Success

Harrison’s standing as a top prospect peaked back in 2023, when he cracked the top 20 on some top 100 prospect rankings across the industry and became the top left-handed pitching prospect in the game.

Upon his first taste of big-league action, Harrison tossed to a low-4.00s ERA in seven starts with the Giants in 2023. The following year was less than stellar, as his ERA saw a bump up to 4.56 across 124.1 innings as a 22-year-old.

2025 is where things got interesting for Harrison. He got off to a suboptimal start that year, posting another 4.56 ERA across his first 23.2 innings and eight appearances (four starts). Command remained a growing concern, and he had yet to take the step forward that the Giants were envisioning.

He was then traded to the Boston Red Sox as the headliner for Rafael Devers on June 15, 2025. From there, Harrison spent the following three months with Triple-A Worcester before earning a late-season call-up by the Red Sox. Harrison made three September appearances with Boston (two starts) to the tune of a 3.00 ERA across 12 innings.

Then, in what was deemed a rather surprising move for both parties back in February, Boston moved Harrison to Milwaukee in exchange for infielders Caleb Durbin, Andruw Monasterio, and Anthony Seigler. Through the first month of the 2026 season, that trade is working out in the Brewers’ favor.

The Brewers are widely viewed as one of the best organizations in baseball in terms of pitching development and optimizing their arm talent. The trade they made, parting ways with their presumed starting third baseman in Durbin to acquire an MLB-ready project, told the rest of the industry everything it needed to know about the club’s feelings on Harrison.

This was a pitcher with plenty of arm talent and prospect pedigree who has yet to get a real shot to reach his potential in the majors. Well, Milwaukee has given him that opportunity from the get-go this season, and thus far, he has passed the test with flying colors.

What’s Helped Harrison Unlock a New Level?

The Brewers are notorious for developing arsenals, primary leaning into several variations of fastballs. Sticking with Priester as an example, the Brewers had him shelve his four-seam last season — a pitch that, frankly, wasn’t very good — and had him up his sinker and cutter usage to keep hitters off balance.

Priester is far from the only example of this blueprint; the foundation of Milwaukee’s pitching development is built upon this philosophy of developing arms.

But their approach with Harrison has been slightly different.

Harrison’s fastball has always been his bread and butter. The highest-graded pitch of his arsenal as a prospect, his success always hinged on the performance of his four-seam. But instead of making Harrison into a pitcher that he isn’t, they’ve embraced his outlier fastball characteristics in order to put him in the best position to succeed.

The Brewers actually have had Harrison completely shelve his cutter entirely this season. Instead, they have worked on developing his changeup while enhancing his slurve to help him attack both righties and lefties more efficiently. The early results have been extremely encouraging.

A Redefined Arsenal

Starting with his arm slot, the Brewers have moved Harrison’s arm slot up from 27° last season to 33° this year. It’s the highest his arm slot has been in his career and his highest since it sat at 30° as a rookie back in 2023.

As a result, Harrison is getting more vert on his four-seam fastball than he ever has while maintaining the incredible arm-side run that makes it such a good offering.

The pitch is currently getting 15 inches of induced vertical break, over two and a half inches more than in 2025, to go with a whopping 13 inches of arm-side movement. It’s just over an inch less of run when compared to a season ago, but that’s still strong movement that is paired with a noticeable uptick in IBV. At a mid-90’s velocity (94.6 mph), the pitch continues to be a serious weapon for Harrison.

Among the 22 qualified arms who generate at least 13 inches of arm-side run with their four-seamer, Harrison is one of four names who also generate 15 or more inches of IBV on the pitch. Grading out with a Stuff+ score — a model that grades the physical characteristics of a pitch, such as release point, velocity, movement, and spin — of 106, that matches the fastball grades of aces such as Yoshinobu Yamamoto, Jacob deGrom, and Chris Sale.