Why Tyler Glasnow’s four-seam fastball acts like a cutter

Does Tyler Glasnow throw a traditional four-seam fastball or a cutter?

The answer is both simple and not, as Brian Menendez investigated earlier this month.

Glasnow’s grip is decidedly a traditional four-seam, his large hands are on all four seams in any photo or broadcast slo-mo, but put in action and you get viral strikeouts with a high-90’s occasionally cutting fastball:

I asked; it’s on purpose.

“I usually always have a cut on it, sometimes more so than others,” Glasnow told me earlier this month when the Rays were in Toronto. “I have a weird — I don’t know what it is. It’s on the four-seam, but my fingers have always been curved, I hold it wide.”

Glasnow holds everything wide, because he doesn’t just hold the baseball, his fingers wrap around the baseball. This is the consequence of the 6’7” Glasnow having massive hands: It’s just what the fastball does, without any consciously added finger or thumb pressure, or deviation from the standard grip. He knows when it’s going to cut more or less. “If I really want it to, I can kind of just rip it a little harder, and it usually just cuts more.”

It’s possible the length of his arms adds to the effect as well. “I’ve found I’m linear [to the plate], but I also come around it,” Glasnow explains, demonstrating his throwing motion, causing a couple players to need to dip out of the way in the narrow Toronto visiting clubhouse. “I’ve thrown like that my whole life.”

Like any good pitcher, Glasnow is a student of his own game, and it’s clear he is becoming a master.

To watch Glasnow demonstrate his pitch grips reminded me of working with elementary school kids on how to throw a Little League regulation size baseball. Not only was I being given a welcomed lesson, but to see a pro-size baseball in his hand versus my own seemed like the difference between holding a mandarin and a grapefruit.

Photo by Jonathan Daniel/Getty Images

Throwing the baseball the way his body naturally wants to throw seems to be the secret to success for Glasnow, who worked with his similarly-sized pitching coach Kyle Snyder throughout the offseason.

What the Pirates may have tried to change, Snyder seems to have relaxed, allowing the player to not overthink what he already does well, particularly when it comes to the fastball movement.

“My whole early pro-ball was me trying to get rid of it. I was always trying to, because it was hard for me to throw strikes.” Glasnow explained the Pirates mentality as, “If I can eliminate the cut and get it to go straighter, maybe I can throw more strikes.”

It didn’t work; Glasnow had a double-digit walk rate almost every stop in his minor league career, and in the majors averaged a 13.9% walk rate across three seasons of attempts in Pittsburgh (141 innings) before he was traded to the Rays.

This year, Glasnow has a 5.4% walk rate over his first five starts, and is sporting a 1.53 ERA, the lowest in the American League among qualified pitchers.

For Glasnow to find success, it was all about harnessing the natural fastball movement and building a strategy around it. “If it’s late in the count, usually like an outside fastball — anything my gloveside — it’s usually more prone to cut that way.” And so he does.

The Rays are harnessing his natural fastball movement to fool hitters a bit more. The cutting action on his four-seam fastball is what the baseball does — “It’s always just been like that. I can’t not do it!” — and there’s no point in fixing what isn’t broken.