Tyler Glasnow has a plus fastball — a somewhat-unique plus fastball — and he relies on it heavily. The Tampa Bay Rays righty is throwing it 66% of the time, the fourth-highest rate among qualified pitchers. A four-seamer delivered from Glasnow’s towering 6-foot-8 frame, the offering has an average velocity of 96.6 mph. It’s the pitch you’re going to read about here.

When I approached him on Saturday, I’d actually been thinking about his changeup. While it’s a pitch Glasnow throws infrequently, the always-insightful Daniel Russell wrote about it recently at Drays Bay, and I was intrigued. When I’d spoken to Glasnow last August, we talked primary breaking balls; his seldom-used change-of-pace wasn’t even mentioned.

Glasnow threw me a changeup on Saturday. When I suggested it as a topic, he said we should talk about his fastball instead, for the aforementioned reason: he rarely throws his changeup.

The following day, Glasnow threw nine of them in a dominating performance against the Red Sox at Fenway Park. That’s as many changeups as he’d thrown in his first five starts combined; hence his subterfuge. It was part of the plan going in.

Is it also his plan going forward? I asked that question following the game.

“It depends, really” responded the erstwhile Pittsburgh Pirate. “We’ll game-plan before. If I need to mix it in — if it’s a good matchup for some of the hitters — for sure. I think it was especially effective today, because I didn’t throw it at all against them last week.”

More changeups than usual didn’t mean fewer fastballs. Of the 101 pitches Glasnow delivered in Sunday’s outing, 70 were of the four-seam variety — more specifically, a four-seamer with cutting action that he’s learned to embrace.

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Tyler Glasnow: “I’m a power pitcher. My emphasis is on velo, spin rate, spin efficiency, carry — just efficiency of the fastball in general. I have a different fastball grip. My fingers are curved, and I cut the ball. I’ve always had a pretty wide grip on my fastball, and that’s kind of been the reason I cut it.

Tyler Glasnow’s fastball grip

“When I was younger — when I was in the minor leagues — I tried to eliminate that cut. That’s because I walked guys. It was, ‘OK, I need to start from the bottom; how can I reset and get guys out in the zone?’ The cut was hard to control — this is when I wasn’t as in control of my body — so I thought it should go. I have more control over my delivery now. I’ve got to a point where the confidence is there to put any pitch in the strike zone if I throw it with conviction. Now I embrace the cut.

“It’s not a cutter. Sometimes it will cut more, and sometimes it won’t, but generally … I mean, if you get the Edgertronic camera behind it, I’m not a true, 100%-efficiency guy. By that, I mean right behind it; I’m on the side of it a little bit. And because the cut is natural, it can be a little different. Some days it acts more like a true cutter, while other days it’s more like a sweeping cutter.

“I can still get carry. Certain fastballs are different. If I’m going arm side, it doesn’t cut as much, and there’s a lot more carry. So I’m trying to … in a way, I have two different fastballs. If I want it to spin straight, I can make it spin straight. My carry can increase a little bit. [Pitching coach] Kyle [Snyder] and I worked on carry a lot this past offseason. We worked on what you really need to do to have optimal efficiency, optimal carry. But again, my glove-side fastballs will generally have more cut.

“That said, I do have control over it. Like I said, if I want the ball to go straight — straight with carry — I can make it go straight. If I’m out there just competing, it’s going have the natural cut. But if I want to throw an up-in-the-zone heater — something with carry to play off my curveball — I can make it go straight. That goes for glove-side, as well.

“It’s a matter of — and I’m so happy that I learned this over the offseason — thinking about it in terms of efficiency, and where my hand is placed behind the ball. I didn’t change anything mechanically, or through my delivery. If I want it to go straight, I’m more directly behind it. If I just want to throw a normal fastball — for me, a fastball that cuts — I just don’t think about it all, I’m just with my natural more-on-the-side of the ball. Basically, it’s all about how the ball is coming off my fingers. That’s all it really is.”