"He's giving me feedback," said Cosart, whose next start is Thursday night at Seattle. "I'm working on throwing a sinker now, and he's helping me. It's just [the] constant reinforcement that we do as a staff."
Since his Major League debut on July 12, 2013, Cosart ranks 10th among American League pitchers with at least 100 innings in ERA (3.02) and BAA (.231). Relying mostly on his fastball and curve, he ranks eighth this season in the AL in ground ball-to-flyball ratio (2.10).
"If he could add that [sinker] to what he's already got, it would be something," Feldman said. "Not many have three plus-pitches."
Earl Bloom is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.