Automated Ball-Strike System

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.{{cite news |last1=Maaddi |first1=Rob |title='Robot umpires' debut in independent Atlantic League |url=https://apnews.com/article/93f7e8be7f404ff2a6eadf2e9295c9d3 |access-date=February 21, 2025 |work=AP News |date=July 11, 2019 |language=en}}

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.{{cite news |last1=Brandt |first1=David |title=MLB's top prospects deal with good, bad of 'robot' umpires |url=https://apnews.com/mlbs-top-prospects-deal-with-good-bad-of-robot-umpires-2972799c8928483c92156c182909625b |access-date=February 21, 2025 |work=AP News |date=October 24, 2019 |language=en}}

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.{{cite news |last1=Blum |first1=Ronald |title=Automated strike zone coming to minors but a while from MLB |url=https://apnews.com/article/technology-mlb-baseball-rob-manfred-minor-league-baseball-fd64782047ad44f447e272375c712da5 |access-date=February 21, 2025 |work=AP News |date=March 17, 2021 |language=en}}

Five Triple-A baseball stadiums used ABS in 2022, and the system expanded to all stadiums at that level in 2023.{{cite news |title=MLB on track to expand robot umps to all Triple-A ballparks |url=https://apnews.com/article/mlb-sports-rob-manfred-c4c8746bc3be2e932f109fc91cff6f81 |access-date=February 21, 2025 |work=AP News |date=January 13, 2023 |language=en}} 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.{{cite news |last1=Golen |first1=Jimmy |title=Robo umps reach Triple-A, but MLB rollout still uncertain |url=https://apnews.com/article/robo-umps-abs-triplea-ccc901dc69c6101fb6a793e5fe867a77 |access-date=February 21, 2025 |work=AP News |date=May 9, 2023 |language=en}} 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.{{cite news |last1=Blum |first1=Ronald |title=MLB switching to challenge system full-time for robot umpires experiment at Triple-A |url=https://apnews.com/article/robot-umpires-mlb-0e656caa19bb84d30916afb1070c5a4f |access-date=February 21, 2025 |work=AP News |date=June 18, 2024 |language=en}} In 2024, 51% of challenges in Triple-A games were successful.

The KBO League started to use ABS in its 2024 season.{{cite news |last1=규빈 |first1=홍 |title=KBO, 2024시즌부터 자동 볼 판정 시스템·피치 클록 도입 |url=https://www.yna.co.kr/view/AKR20231019104400007 |access-date=October 19, 2023 |work=연합뉴스|lang=korean }} Unlike in MLB, KBO uses ABS to call balls and strikes automatically.{{cite news |last1=수현 |first1=최 |title='0.78㎝ 차이' 칼같은 판정… '로봇 심판'이 야구를 바꾼다 |url=https://www.chosun.com/opinion/2024/05/03/HMOTI4H7XNG2ROTADG7IECVO7M/ |access-date=May 3, 2024 |work=조선일보|lang=korean }}

ABS was 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.{{cite news |last1=Castrovince |first1=Anthony |title=MLB to test automated ball-strike challenge system during spring games |url=https://www.mlb.com/news/automated-ball-strike-calls-mlb-spring-games |access-date=February 21, 2025 |work=MLB.com |date=February 18, 2025 |language=en}}

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 {{convert|19|in|mm}} in 2022, then decreased it to {{convert|17|in|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, {{convert|8.5|in|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.{{cite news |last1=Blum |first1=Ronald |title=Robot umpires are getting their first MLB test during spring training |url=https://apnews.com/article/mlb-robot-umpires-abs-9034454b5a795262bf97446ff38d0361 |access-date=February 21, 2025 |work=AP News |date=February 20, 2025 |language=en}}

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.{{cite news |last1=Castrovince |first1=Anthony |title=MLB to test automated ball-strike challenge system during spring games |url=https://www.mlb.com/news/automated-ball-strike-calls-mlb-spring-games |access-date=February 21, 2025 |work=MLB.com |date=February 18, 2025 |language=en}}

MLB started testing ABS because of fans' strong feelings about inaccurate umpire calls of balls and strikes, which can affect the outcome of games.{{cite news |last1=Sullivan |first1=Becky |title=Everything to know about the MLB's ball-strike challenge system at spring training |url=https://www.npr.org/2025/02/20/nx-s1-5304103/mlb-ball-strike-umpire-abs-challenge |access-date=February 21, 2025 |work=NPR |date=February 20, 2025 |language=en}} 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.{{cite news |last1=Rogers |first1=Jesse |title=When and how will robot umps arrive in the majors? Latest on MLB's plan |url=https://www.espn.com/mlb/story/_/id/40377683/mlb-robot-umpires-automated-balls-strikes-challenge-system-umps-majors |access-date=February 21, 2025 |work=ESPN.com |date=June 18, 2024 |language=en}}

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.{{cite news |last1=Booth |first1=Tim |title=MLB catchers wary of looming robo umps amid rules changes |url=https://apnews.com/article/mlb-sports-minnesota-twins-rob-manfred-jose-trevino-063f72484e37a99e6ff428aaaf156d2d |access-date=February 21, 2025 |work=AP News |date=February 24, 2023 |language=en}} 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".{{cite news |last1=Stark |first1=Jayson |title=Robot umps are here: What MLB players need to know to navigate ABS this spring |url=https://www.nytimes.com/athletic/6144194/2025/02/20/abs-robot-umps-mlb-spring-training/ |access-date=February 21, 2025 |work=The New York Times |date=February 20, 2025}}

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.{{cite news |last1=Drellich |first1=Evan |title=The robo ump could cause a unexpected casualty: the TV strike zone box |url=https://www.nytimes.com/athletic/6145712/2025/02/19/robo-umps-tv-strike-zone-box-mlb/ |access-date=February 21, 2025 |work=The New York Times |date=February 19, 2025}}

{{reflist}}

• Instant replay in Major League Baseball

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