ARLINGTON — Here’s the deal: Statcast classifies Kumar Rocker’s nasty breaking pitch as a slider. He calls it a curveball and a “slider at times.” It was the most effective tool in his Texas Rangers debut Sept. 12 against the Seattle Mariners and secured five of his seven strikeouts.
So which, exactly, is it?
“A little bit of both,” Rocker said Wednesday at Globe Life Field.
It plays that way too. Rocker’s “slider” carried an average of 42 vertical inches of drop in his major league debut against the Mariners. The average vertical drop of a curveball, for reference, is anywhere from 40 to 70 inches. Only 10 qualified starting pitchers threw a slider with as much vertical drop as Rocker this season, according to Baseball Savant. None, however, has as few inches of horizontal break as Rocker’s (0.9 inches).
Of all pitchers who’ve thrown 100-plus sliders this season, only 26 have averaged more vertical drop than the Rangers’ 24-year-old rookie, and only two — Houston’s Bryan Abreu (86.2 mph) and Tampa Bay’s Pete Fairbanks (85 mph) — throw theirs as hard or harder than Rocker, who’s “slider” averaged 85 mph against Seattle, though Abreu’s and Fairbanks’ sliders move horizontally more.
The best comparison among starting pitchers? Philadelphia’s Cristopher Sánchez, whose slider (84.4 mph, 41.6 inches of drop, one inch of horizontal break) has held opponents to a .226 batting average. Rocker’s has more spin (2,251 rotations per minute compared with 2,022) and generated a ridiculous 61.9% whiff percentage against the Mariners. No qualified pitcher in baseball has garnered a higher whiff rate with a slider this season.
It might best mirror the hardest-thrown curveballs leaguewide this season (in the 85-87 mph range), with each carrying an average vertical drop of anywhere from 38 to 50 inches. Even those, though, tend to yield more horizontal movement.
Rocker’s pitch may be in a unique class. It will undoubtedly be on display Thursday when Rocker is scheduled to make his second major league start and first at home when he faces the Toronto Blue Jays. Rangers manager Bruce Bochy said Rocker could throw “fairly close” to 85 pitches.
“Being a home debut with the team that drafted you, took a chance on you, I think there’s definitely going to be nerves,” said Rocker, who pitched four innings of one-run ball at Seattle in his debut. “You want to do the best for them, and you hope to get a win out of it as well.”
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