This Tigers prospect has two knuckleballs -- one that nears 90 mph and another called 'Yoshi'

PEORIA, Ariz. – Many pitchers seek out velocity. Others look to induced vertical break or spin rate. Tigers knuckleballer Kenny Serwa seeks out a different metric when he’s on the mound.

It’s a little less scientific.

“I look for the catcher to miss the ball,” he said. “That's the only way I can tell if they're really moving, really dancing. If he's catching them, I’m like, ‘Dang it, is it not moving?’ I'm asking the guys behind me, ‘How was that?’ They’ll say it’s good, but I look for him to drop the ball.”

The 28-year-old popped onto the radar for many last offseason when he went viral for touching 88.5 mph with his knuckler during a Tread Athletics pro day showcase. Serwa, who spent time in the independent Pioneer League and American Association, signed a Minor League deal with Detroit on Jan. 22 and posted a 3.58 ERA with 84 strikeouts in 118 innings between High-A West Michigan and Double-A Erie in his first season of affiliated ball. The Tigers sent him to the Arizona Fall League, where he joins big-name prospects Kevin McGonigle and Max Anderson for extra work in the desert.

After Serwa’s AFL debut on Oct. 14, MLB spoke with the hurler about how he makes it work as a knuckleballer in 2025 and what else he brings to the table in his arsenal:

Serwa’s genesis with the famed low-spin pitch came when he was around 9 or 10 years old. His father noticed him throwing in the front yard and working with some potential breaking balls. Fearing for his son’s arm health, Ken Serwa told the preteen he had to back off expanding his repertoire in that way.

“I didn’t even have any facial hair yet, that’s what they said back in the day,” said the younger Serwa. “So he told me no breaking balls.”

His dad offered an alternative that would be much less taxing on the arm: the knuckleball. He originally taught it with the knuckles literally on the baseball, and there was one early promising indication that there was something there.

“I started throwing it and hit him in the chest actually,” Serwa said. “So it was pretty cool.”

The grip has changed over the years. Serwa now digs the tips of his fingers and his nails into the ball itself, avoiding the seams, to create the dancing motion that has put him two stops away from The Show.

And it’s been a winding road to get there in the first place.

Serwa started his collegiate career with two years at Division II St. Joseph’s College, making only one appearance in that span, before transferring to SIU-Edwardsville. He lasted three years there, including the shortened 2020 spring in which he owned a 1.33 ERA and led the Ohio Valley Conference with a 14.0 K/9, before getting chances at Central Florida (2021) and Dayton (2022) – all the while trying to show why he could follow in the footsteps of Phil Niekro, Tim Wakefield and R.A. Dickey.

The opportunity came, in part, thanks to the internet.

The 88.5 mph viral knuckleball would be the fastest in the pitching tracking era (since 2008). Padres lefty Adrian Morejon has thrown a knuckle-change up to 88.3 on Aug. 10, 2024, while his fellow San Diego hurler Matt Waldron maxed out at 84.9 with a more traditional version of the pitch on June 30 this year.

That elite level of velocity in a showcase setting hasn’t exactly translated to pro ball. Synergy Sports recorded Serwa’s fastest knuckleball at 86 mph in season, and in that first Fall League outing, he topped out at 82.6. That’s by design from the Tigers, who were impressed by Serwa’s velo in that Tread video but want him pitching more to the situation than the TrackMan readings.

“There are definitely times in games when I see that hard knuckleball sign, and I’m like, ‘Ooh, I could rear back,’” Serwa said. “But it’s more so just about mixing up the timing and making sure that with the count and everything that we throw it over the plate. I could rip them and potentially throw them harder, but we have to make sure they’re over-the-plate, competitive pitches. If the speed varies a little bit, it varies a little bit.”

That “hard knuckleball” designation is an important one because Serwa actually has two versions of his trademark pitch. The other one – a slower version in the 70s – is called the Yoshi, named after the Nintendo character who throws a similar pitch in Mario Super Sluggers (with maybe a few more video-game effects).

“It’s just a feel thing,” Serwa said. “Depending on what type of swing I saw with the slower one or the harder one. If he’s seen the fastball or something a little faster than the slow one I like to change the speeds, almost like a changeup. If he’s seen the breaking ball, it’s very similar in speed [to the slow one], so I like to throw it a little bit harder.”

It comes down to intent. The harder knuckleball comes with a little more arm speed, which in turn comes with a little more spin – though all of Serwa’s knuckleballs on Oct. 14 came under 600 rpm. The softer version has less spin and more dance; one against Top 100 prospect Cam Collier registered only 70 rpm, with the Reds prospect lunging with a hapless swing on a pitch on the outside corner.

With those two versions, Serwa is making one of the most fascinating pitches in baseball his own. But the Tigers don’t want him losing sight of history, and director of pitching Gabe Ribas got Serwa in touch with 25-year Major Leaguer Charlie Hough, who has worked with the next generation at Knuckleball Nation in California.

“His biggest piece of advice was just being consistent with your motion as a knuckleballer,” Serwa said. “Like every little tweak of motion can influence the ball a little too much to sway the ball outside the plate, outside the strike zone. [It’s about] being consistent, making sure we're being the same on every pitch, being consistent with our landing.”

As much as the knuckleball will garner attention in Arizona and beyond, Serwa will also sprinkle in four-seamers, sinkers, cutters and curveballs to keep hitters honest. The heaters will only sit 89-91 typically, but that comes in a lot more like a buzzing bee when you’re expecting a floating butterfly.

Alfredo Duno – another Top 100 prospect from the Reds organization – can attest after he whiffed on an 89.9 mph sinker for strike three after seeing a first-pitch sinker, two knuckles and the curve previously in the second-inning at-bat of Serwa’s AFL opener.

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“Some guys don’t like when a fastball is kind of an offspeed pitch, per se,” Serwa said.

From Trey Yesavage’s armside arsenal to Payton Tolle’s massive extension, sometimes the best thing a pitching prospect can be is unique. That remains Serwa’s goal in the desert, where he’ll try to keep hitters and his own catchers off-kilter alike.

“Keep the knuckleball going, and just keep working at it,” he said. “That’s basically what I’m doing out here – getting as many reps as possible.”