Overview
A checked swing ruling determines whether a batter who attempted to hold back committed to the swing enough to warrant a strike call. The official rules lack a precise definition of a swing; umpires are variously said to look at whether the bat crossed the front plane of home plate or whether the wrists rolled over, yet neither yardstick is written into the rules, so the call relies heavily on umpire judgment. When the home plate umpire calls a ball, the defensive team may appeal to the base umpire (first or third base), who can overturn the call to a strike. This two-stage process is among baseball's most contentious areas, frequently criticized for inconsistency. MLB introduced an Automated Ball-Strike (ABS) challenge system built on Hawk-Eye tracking for the 2026 season, but what a team may send for review is the home plate umpire's ball and strike call; the system does not adjudicate whether a batter swung. NPB, as of August 2026, has not adopted that kind of technology at all, so checked swings there are still decided by the umpire's eye.