TheAutomated Ball-Strike System (ABS) is a system to automate the interpretation of whether pitches are in thestrike zone inbaseball games. It has been used by severalminor leagues and will be used inMajor League Baseball (MLB) starting in2026.[1]
The independentAtlantic League first used ABS, nicknamed "robot umpires", during its 2019 all-star game.Umpires used earpieces to receive ball-strike calls usingTrackMan 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.[2]
TheArizona Fall League began using ABS during its 2021 season. The technology drew complaints from players and fans for its treatment ofbreaking 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.[3]
TheFlorida State League, alow-A league in Florida, used ABS in its 2021 season. TheMajor League Baseball Umpires Association (MLBUA) agreed to cooperate and assist if MLB commissionerRob Manfred decided to use ABS at the major league level, as part of the MLBUA's contract with MLB in 2020.[4]
FiveTriple-A baseball stadiums used ABS in 2022, and the system expanded to all stadiums at that level in 2023.[5] 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.[6] 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.[7] In 2024, 51% of challenges in Triple-A games were successful.[8]
TheKBO League, inSouth Korea, started to use ABS in its2024 season.[9] Unlike in MLB, KBO uses ABS to call balls and strikes automatically.[10]
ABS was in place forSpring Training before the2025 MLB season, promoted as theAutomated Ball-Strike System presented byT-Mobile for sponsorship reasons.[11] Thirteen Spring Training ballparks, used as home fields by 19 clubs, are equipped with ABS technology. MLB implemented ABS as a challenge system; human umpires make initial calls, which pitchers, catchers, and batters may challenge.[11]
MLB used ABS for the2025 All-Star Game, with a similar configuration to spring training: each team had two challenges, which could be requested by the pitcher, catcher, or hitter immediately after a call.[12]Cal Raleigh, the first player to request an ABS challenge in an MLB All-Star Game, successfully challenged the umpire's ball call of a pitch he caught fromTarik Skubal, resulting inManny Machado being called out on strikes.Jacob Wilson was the first batter to challenge a call, successfully getting a pitch fromMacKenzie Gore changed from a strike to a ball.[13]
In September 2025, MLB's competition committee approved use of ABS beginning with the2026 season, with similar processes to those used in Spring Training and the All-Star Game. Each team starts with two challenges, retains a challenge if it is successful, and may receive additional challenges in extra innings.[1]
As implemented by MLB, ABS usesHawk-Eye camera technology, and a private5G network byT-Mobile to transmit data. Reviews are shown on screens in stadiums and on broadcasts for home viewers.[14]
MLB has experimented with the size of the strike zone, a three-dimensional space defined in theofficial 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.[8]
In MLB, only the batter, pitcher, or catcher may challenge a ball or strike call by tapping his 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.[1] In extra innings, a team that begins an inning with no challenges will receive one challenge to use or carry forward; they will not receive additional challenges if they have at least one at the start of an extra inning.[15] Players must make a decision on their own, without assistance from other players or team personnel, such as coaches or managers. Unlikeinstant replay challenges, managers may not challenge a ball-strike call.[11]
MLB started testing ABS because of fans' strong feelings about inaccurate umpire calls of balls and strikes, which can affect the outcome of games.[16] 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.[17]
Players and managers have sometimes objected to ball-strike calls even after an ABS review, but doing so still risksejection from the game. "Nobody complains about anything anymore with the strike zone because there's nothing to complain about," saidToby Gardenhire, manager of theSt. Paul Saints.[6] Players observed that catchers could no longerframe pitches to try to get strike calls on pitches outside the zone.[18] 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", saidMichael Toglia of theColorado Rockies, about calling a challenge during his time in Triple-A.[16]Tyler Glasnow of theLos 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".[19]
Baseball broadcasters have had to redesign theirdigital 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.[20]