Brozdowski: Do sliders cause pitchers to lose their curveball feel?

From Lance Brozdowski at Baseball Prospectus on April 2, 2019:

Shortly before the Nationals traded pitching prospect Lucas Giolito to the White Sox in a package for Adam Eaton, the 6-foot-6 right-hander had started working on a slider. He would debut the offering for the Triple-A Charlotte Knights the following April after an offseason of refinement. To this day, it remains an important lateral complement to the exceptional vertical break on his curveball. For a period of time while learning his slider, however, Giolito lost the feel for his curveball.

“If you’re so used to doing it one way to manipulate the spin on a ball, when you try and introduce the other [way], both of them can kind of get lost in the mix,” Giolito told me during spring training. “You’ll end up throwing one pitch, which is kind of like a slurve—not very good.”

For Giolito, throwing a slider involves staying on top of the ball and coming down the side to create spin and glove-side horizontal movement. For a curveball, he turns his hand over completely, like most pitchers, creating top spin rather than the side spin of a slider. The motions seem distinct, but muddling can still occur.

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Originally published: April 2, 2019. Last Updated: April 2, 2019.