Devin Smeltzer, Spin Rate, and the Unknown

On Monday afternoon, Devin Smeltzer pitched for the Twins in a Grapefruit League contest with the Cardinals. Thanks to several different forms of defensive deficiency, St. Louis scored four times in Smeltzer’s two frames, but he had two strikeouts and no walks. Lewis Thorpe’s brief personal absence has opened a narrow window of opportunity for Smeltzer to start the season as the Twins’ fifth starter. That could turn out to be enough, if Smeltzer can make a few adjustments to make his similarities to one new teammate play up.

With an average fastball velocity of just 89.1 miles per hour, Smeltzer starts at a certain disadvantage, even as a lefty. However, his average fastball spin rate in 2019 was 2,433 revolutions per minute, a number as far above the league average as his velocity is below it. A budding modern heuristic for capturing the value of fastball spin rate is the Bauer Unit, named after Reds right-hander Trevor Bauer. Divide a hurler’s average spin by their average velocity, and you get their Bauer Units for a given pitch. The league average for Bauer Units on the fastball hovers around 24. Smeltzer sits at a very impressive 28.3. One of the few pitchers who topped that figure last year: Rich Hill, at 28.4.

Smeltzer shares more in common with Hill than handedness and those fastball spin characteristics. Though Hill came up as a heralded prospect and was a solid big-leaguer for a couple of years, this version of him emerged only after a long sojourn in the minors and independent leagues, and after a stint as a matchup reliever. Smeltzer was similarly shoved into a relief role before he attained the majors, but being traded to the Twins gave him a fresh start. Both have overcome significant adversity, on and off the field, to get as far as they have. Both have extremely impressive spin not only on their heaters, but on their curveballs.

Thus far, however, Smeltzer hasn’t missed bats and shown the ability to dominate the way Hill has, and it’s not hard to see why. Whereas Hill famously launches himself down the mound and comes right over the top with his high-energy delivery, Smeltzer’s deceptive, short-stride windup gives way to a three-quarter arm action. It helps keep batters off-balance, and it has been Smeltzer’s preferred arm slot since he was an amateur. However, that arm angle creates some wasted spin, and some spin that flattens out his fastball into a pitch with more lateral run than vertical hop. It also turns his big, slow curve into a two-plane breaker, rather than a 12-to-6 offering.

Raising his arm angle could transform Smeltzer from a decent pitch-to-contact, control-oriented swingman into a higher-upside guy with the ability to rack up strikeouts. It would unlock the maximum value of his excellent ability to impart spin. Alas, it’s not nearly that simple. For one thing, Smeltzer has gotten to this point despite his lack of pure stuff, and it might be difficult for him to clear the mental hurdle of giving up his unique delivery for a more trendy one, thereby risking the deception he creates by pitching the way he does. For another, it might turn out that his ability to generate that spin is dependent upon his pitching from the angle he uses now—that his current mechanics fit his natural biomechanical signature, in a way throwing from a higher angle never could.

If he runs into further adversity and ends up back in Triple-A for an extended period, Smeltzer might experiment with a change in mechanics. If the Twins end up needing him as a starter or a high-leverage reliever, they might approach him and suggest such tweaks. In the meantime, despite the potential benefits of such a change, it’s hard to see it actually happening. The fear of the unknown, and the possibility that making a change before it’s absolutely necessary could ruin a good thing, will give both parties pause.

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