NEW YORK – Robot umpires are set to debut in Major League Baseball this year.
The Automated Ball/Strike System will function as a challenge process where human umpires make the initial calls, which can be reviewed by a computer system. This technology has been trialed in the minor leagues since 2019, with implementations at Triple-A games since 2022, followed by MLB spring training and the 2025 All-Star Game in Atlanta.
Here’s an overview of MLB’s robot umpire initiative.
How the Automated Ball-Strike System Operates
Stadiums will be equipped with cameras that monitor pitch trajectories to determine if they pass through the strike zone. Initially, umpires wore earpieces to receive calls of “ball” or “strike,” which they would then convey using traditional signals.
The Challenge Mechanism
Under the challenge system, umpires continue to call every pitch, but each team can contest two calls per game. If a challenge is unsuccessful, teams get an extra challenge for each extra inning they play. A team can retain its challenge if a call is overturned, similar to the video review process established for home run calls in August 2008 and expanded in 2014.
Technical Aspects of the System
The technology relies on a Hawk-Eye system, which assesses pitches based on each player’s height (measured without shoes). Measurements will occur in the mornings during spring training to ensure consistency, as height can fluctuate throughout the day. MLB expects calibration to take less than a minute for each player.
Strike Zone Configuration
The designated strike zone for the ABS has seen multiple adjustments. Originally set at 19 inches in 2022, it was narrowed to 17 inches, equal to the width of home plate, which resulted in more walks but minor changes in strikeout rates. The top of the strike zone has been adjusted from 51% to 53.5% of a batter’s height for 2024 following pitcher requests.
Challenges and Success Rates
The success rate for challenges in the minors has remained around 50%, with the most recent Triple-A season recording a slight drop. Challenges per game have increased, particularly in late innings, with pitchers’ calls facing more scrutiny as the game unfolds.
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