Which rule system using helmet or cap taps began in MLB in 2026?

The Automated Ball-Strike System, or ABS, began MLB use in 2026 as a challenge-based rule system involving helmet or cap taps.

Under the approved format, a human umpire still makes the initial ball-or-strike call. A pitcher, catcher or batter can immediately challenge that call by tapping the top of the helmet or cap. The tracking system then checks whether the pitch crossed the electronic strike-zone boundaries, and the ruling is changed when the challenge succeeds.

MLB tested versions of automated strike-zone technology in the minor leagues, spring training and special events before approving the challenge system for the 2026 season. Each team began with two challenges and retained a challenge when successful, with additional challenges available in extra innings.

ABS is commonly confused with Statcast, Instant Replay or PitchCom. Statcast supplies tracking data, Instant Replay reviews other plays, and PitchCom helps communicate pitch selections; none is the helmet-tap ball-and-strike challenge system.