Looking ahead to MLB's new Ball-Strike Challenge System
The Joint Competition Committee last September voted to bring the Automated Ball-Strike (ABS) Challenge System, powered by T-Mobile, to the big leagues in 2026 following several years of experimentation in the Minor Leagues and use in MLB Spring Training and the All-Star Game in 2025.
Considered a middle ground between so-called “robot umps” that could call every ball and strike and the long-standing tradition of the natural human error that comes with human umps, the ABS Challenge System gives teams the opportunity to request a quick review of some of the most important ball-strike calls in a given game.
Big league umpires call roughly 94% of pitches correctly, according to UmpScorecards.
How Does It Work?
- Each team will get two challenges and can keep them if they're successful.
- Challenges can only be initiated by a pitcher, catcher or batter, and the request must come right after the pitch.
- To signal a challenge, the pitcher, catcher or batter will tap his hat or helmet to let the umpire know. No help from the dugout or other players on the field is allowed.
- In each extra inning, a team will be awarded a challenge if it has none remaining entering the inning.
Because challenges can be lost, it is incumbent upon the player to be judicious about asking for a challenge (i.e., not “wasting” it in a low-leverage spot so that it is available to his team in a high-leverage spot). So, in that sense, the ABS Challenge System adds strategy to the sport.
Technology
The ABS system uses similar technology to the line-calling system in tennis, with 12 cameras in each ballpark tracking the ball with a margin of error around one-sixth of an inch. The ABS zone will be a two-dimensional plane in the middle of the plate that spans its full width (17 inches). The zone's top will be 53.5% of a player's height and the bottom 27%.
The system runs on a 5G private network from T-Mobile for Business’ Advanced Network Solutions. With Hawk-Eye technology running in the background and monitoring the exact location of each pitch, relative to the batter’s zone, players can request a challenge of a ball or strike call they feel the umpire got wrong.
When a call is challenged, the Hawk-Eye view is then transmitted over a 5G private network from T-Mobile’s Advanced Network Solutions and nearly instantaneously shown to those in attendance via the videoboard and to home viewers via the broadcast. The ball-strike call is then either confirmed or overturned, and the game goes on having only been briefly interrupted.
The Strike Zone
Knowing the zone will become a new soft skill, especially because the zone’s vertical limits will be different for each hitter. The ABS zone for each player is based on measurements taken by one independent party and verified by another; the top of the zone is defined as 53.5 percent of a player’s height and the bottom of the zone is 27 percent of their height. The zone is 17 inches wide -- the width of home plate -- and pitch location is measured at the midpoint between the front and back of the plate. Any part of the ball only needs to tick the edge of the zone to be a strike.
Testing
The full ABS system was first used in the independent Atlantic League in 2019. The Challenge System was first used in the Florida State League in 2022. During the 2023 and 2024 Triple-A seasons, both the Challenge System and full ABS were tested. By the end of 2024, full ABS had been pushed aside in favor of the Challenge System, which continued to be used in 2025.
The league changed the height criteria several times while experimenting in Triple-A games over the past three years.
Data shows from MLB’s 288-game experiment in spring training in 2025, calls were overturned 52.2 percent of the time; catchers had a 56 percent success rate, compared to 50 percent for hitters and 41 percent for pitchers. There was an average of 4.1 challenges per game, and those challenges took an average of 13.8 seconds.
The Joint Competition Committee consists of ownership management personnel, players and an umpire.
(Sources MLB.com, ESPN.com)