What Is Automated Ball-Strike Judging
ABS (Automated Ball-Strike System) uses high-precision tracking technology to measure each pitch in real time so that a machine can call (or verify) balls and strikes. MLB first trialed "full ABS", with machine calls on every pitch, in the independent Atlantic League in 2019, introduced a challenge format in the Florida State League in 2022, and tested both formats side by side at Triple-A in 2023 and 2024. The challenge format, which drew clearly stronger support from fans and players, survived those trials, and after further tests in 2025 spring training and the All-Star Game, MLB formally decided to adopt it in the majors from the 2026 season. As of August 2026, NPB has made no decision on ABS and announced no roadmap; the players' union asked the league to consider adoption in May 2026.
How TrackMan and Hawk-Eye Work
Two families of tracking technology underpin ABS: radar and optical cameras. TrackMan, a Doppler-radar system, derives ball velocity, spin, and trajectory from reflected radar waves; it served as the core of MLB's Statcast measurement platform from 2015 through 2019. In 2020, Statcast switched to a Hawk-Eye camera system, which reconstructs the ball's flight and player movement by triangulating footage from multiple high-speed cameras. Hawk-Eye, originally developed as an officiating aid for tennis and cricket, is also the technology that tracks each pitch against the batter's strike zone in the challenge system MLB launches in 2026. Camera-based systems are sensitive to lighting and weather, so leagues with many open-air ballparks need careful per-stadium calibration.
Defining the Strike Zone and Why Machines Struggle
The Official Baseball Rules define the strike zone as the space over home plate between the midpoint of the batter's shoulders and the top of the uniform pants, down to the hollow beneath the kneecap. In practice the zone shifts with every batter's height and stance, and how to pin it down mechanically is the central question for ABS. MLB's challenge system fixes the zone as a rectangle 17 inches wide (the width of home plate), with the top at 53.5% of the batter's height and the bottom at 27%. A human umpire's zone is generally rounder and slightly pitcher-friendly, and that gap has itself been a subject of study. Research using pitch-tracking data shows that human accuracy drops near the edges of the zone and that calls drift with the ball-strike count. Machine judging removes those biases, but questions remain: for instance, whether a height-based formula fits batters with extreme crouches equally well.
ABS Experiments Around the World
Korea's KBO was the first league in the world to bring ABS to its top flight, adopting it league-wide from the 2024 season. Calls are relayed to the plate umpire by earpiece, and arguing an ABS call is not allowed; analyses since adoption have reported an increase in strikes called on high pitches. MLB arrives in 2026 with the challenge format: in 288 spring-training games in 2025, teams averaged 4.1 challenges per game, reviews took 13.8 seconds on average, and 52.2% of challenged calls were overturned. NPB, as of August 2026, has not decided on adoption; the players' union formally requested consideration in May 2026. With operational data accumulating overseas, the question for NPB is when to move and which format to choose.
Technical and Institutional Hurdles for NPB Adoption
Bringing ABS to NPB would require a uniform measurement setup across all twelve home ballparks, with substantial installation and maintenance costs (no official estimates have been published). Technically, open-air stadiums pose challenges of weather and sunlight, and each venue would need its own calibration. Institutionally, the role and authority of umpires would have to be redefined, including consultation over how the change affects umpiring careers. As of August 2026, NPB has announced no trial plans or roadmap. The operational record now building up in KBO and MLB will be the key evidence base when NPB weighs its decision.
Future Outlook - A Human-Machine Hybrid Model
MLB formalized its 2026 adoption after the joint competition committee approved the challenge format in 2025. The system keeps the human umpire's call as the default: only the batter, catcher, or pitcher may challenge, immediately after the call, by tapping their cap or helmet, with two challenges per team per game that are retained when successful. MLB chose this middle path over full ABS because minor-league trials showed fans and players clearly preferred the challenge format. Fully automated calling also raises questions of game tempo and the spectator experience, which makes the hybrid model a realistic landing point. If NPB moves ahead, the same balance (better calls without losing the game's traditions) will be the axis of the debate.