# Automated Ball-Strike System

The Automated Ball-Strike System (ABS), known for sponsorship reasons as the Automated Ball-Strike System presented by T-Mobile, is a system to automate the interpretation of whether pitches are in the strike zone in baseball games. In 2025, it is being tested by Major League Baseball (MLB) and has been used by several minor leagues.

## History

The independent Atlantic League first used ABS, nicknamed "robot umpires", during its 2019 all-star game. Umpires used earpieces to receive ball-strike calls using TrackMan technology. Umpires could make a call based on the automated message, or could make their own call if the automated system malfunctioned or registered a call with which the umpire disagreed.
The Arizona Fall League began using ABS during its 2021 season. The technology drew complaints from players and fans for its treatment of breaking balls as strikes even when they break and drop out of the strike zone. Human umpires were obligated to make a call based on ABS, and players could be ejected if they contested a call, as with all ball-strike calls.
The Florida State League, a low-A league in Florida, used ABS in its 2021 season. The Major League Baseball Umpires Association (MLBUA) agreed to cooperate and assist if MLB commissioner Rob Manfred decided to use ABS at the major league level, as part of the MLBUA's contract with MLB in 2020.
Five Triple-A baseball stadiums used ABS in 2022, and the system expanded to all stadiums at that level in 2023. In 2023, Triple-A baseball used ABS with and without a challenge system; without a challenge system, human umpires relayed automated calls, and with the system, an automated call would be used only when a team requested a challenge. In 2024, Triple-A teams that played six-game series first used ABS without a challenge system for the first three games, and with challenges for the latter three; starting on June 25, MLB announced that only the challenge system would be used. In 2024, 51% of challenges in Triple-A games were successful.
ABS is in place for Spring Training before the 2025 MLB season. Thirteen Spring Training ballparks, used as home fields by 19 clubs, are equipped with ABS technology. The system uses Hawk-Eye technology and is a challenge system; human umpires make initial calls, which pitchers, catchers, and batters may challenge.

## Mechanics

MLB has experimented with the size of the strike zone, a three-dimensional space defined in the official rules of Major League Baseball, as used by ABS. The league started with a width of 19 inches (480 mm) in 2022, then decreased it to 17 inches (430 mm), the same width as home plate. The top of the zone was 51% of a batter's height in 2022 and 2023, then raised to 53.5% in 2024 after pitchers' complaints. The bottom of the strike zone was originally set at 28% of the batter's height, and has been 27% since 2022. ABS makes its decision when the ball is at the midpoint of the plate, 8.5 inches (220 mm) from the front and back, despite MLB rules stating that a pitch is a strike if it crosses any part of a 3D solid with home plate as its base. The ABS strike zone does not change based on the batter's stance.
In MLB Spring Training in 2025, only the batter, pitcher, and catcher may challenge a ball or strike call by tapping their cap or helmet immediately after an umpire's call. Each team gets two challenges per game and only loses a challenge if the original call is upheld after review. Players must make a decision on their own, without assistance from other players or team personnel, such as coaches or managers. Unlike instant replay challenges, managers may not challenge a ball-strike call.

## Reaction

MLB started testing ABS because of fans' strong feelings about inaccurate umpire calls of balls and strikes, which can affect the outcome of games. According to an MLB poll in 2024, 61% of team personnel (including players) and 47% of fans preferred a challenge system for ball-strike calls, 28% of team personnel and 30% of fans preferred not to use ABS at all, and 11% of team personnel and 23% of fans wanted full automation.
Players and managers have sometimes objected to ball-strike calls even after an ABS review, but doing so still risks ejection from the game. "Nobody complains about anything anymore with the strike zone because there's nothing to complain about," said Toby Gardenhire, manager of the St. Paul Saints. Players observed that catchers could no longer frame pitches to try to get strike calls on pitches outside the zone. Players in Triple-A have typically saved their challenges for higher-leverage situations; more than 8% of pitches on a 3–2 count were challenged, whereas only 1.6% of first pitches were. "Your heart rate goes through the roof", said Michael Toglia of the Colorado Rockies, about calling a challenge during his time in Triple-A. Tyler Glasnow of the Los Angeles Dodgers said that ABS challenges were "the most fun part of the game" during a rehab assignment in Triple-A, because when a player challenged a call successfully, they felt "vindicated".
Baseball broadcasters have had to redesign their digital on-screen graphics, particularly a rectangle that suggests whether a pitch is in the strike zone, because these graphics do not use the same technology as ABS, and because they could cause fans or teammates to urge a player to request a challenge, in violation of the ABS rules.