A two-seam fastball is a pitch in baseball and softball. Wikipedia

Baseball Pitch Wikidata

A pitch thrown with a grip in the "horseshoe" orientation of the ball, with the rotation at a slight angle resulting in less Magnus effect as compared to a four-seam fastball since only two of the ball's seams cross the flight path; the pitch is delivered with a similar velocity as a four-seam fastball, but has a degree of sink. Wiktionary