KBO's Robot Umpire: How the First League to Fully Use an Automated Ball-Strike System Changed the Game
Since 2024 every ball and strike in KBO first-team games has been called by a system. How ABS works, how players adapted and what it means for baseball's future.
In 2024 the KBO League did something no other top professional league had done: it handed every ball-and-strike call in its first-team games to an Automatic Ball-Strike System, or ABS, better known as the robot umpire.
How the system works
Tracking cameras in the ballpark calculate where each pitch crosses home plate and at what height, and compare it with a defined strike zone. The result reaches the home plate umpire through an earpiece in an instant, and the umpire signals ball or strike accordingly.
The umpire still stands behind the plate, makes the calls, rules on hit-by-pitches and handles plays at home. What the umpire no longer does is judge the pitch.
The top and bottom of the zone are calculated from each batter's height, and its width is set by the plate. Because one system applies one standard, the zone is the same in every game and for every hitter.
Why the KBO did it
Ball-and-strike calls have long been baseball's biggest source of arguments. Two umpires could call the same pitch differently, and a single late-game call could decide a result. Frustration from players and fans damaged the league's image for years.
ABS's biggest change is consistency. Pitchers know a pitch on the corner will be a strike, hitters know a ball will not be called a strike by mistake, and both can focus on the battle between them.
How players adapted
Many players needed time to adjust at first. The system's zone does not match every umpire's habits; high pitches, for example, are more likely to be called strikes. Pitchers who relied on an umpire's tendencies had to rethink their plans, and patient hitters had to relearn the edges of the zone.
The catcher's job changed too. Framing, the art of making a borderline pitch look like a strike, matters far less under ABS, so catchers concentrate more on calling games and blocking pitches.
The future of the game
Korea's experience has drawn attention around the world. After years of testing in the minor leagues, Major League Baseball adopted a challenge system: umpires still call balls and strikes, but pitchers, catchers and hitters can challenge a limited number of calls and have the system check them.
Each approach has its supporters. Full automation is the most consistent; the challenge system keeps the umpire at the centre of the game. What is clear is that technology is changing baseball's most basic contest, the duel between pitcher and batter on every pitch.
What changed on the field and in the stands
One of the first things fans noticed was that arguments over balls and strikes almost disappeared. Managers and players can no longer blame an umpire for a missed call, and the long, heated discussions at home plate that once interrupted games became rare.
Some fans miss the human element; for them a slightly different zone from one umpire to the next was part of the game's character. Others feel that fairness matters more, especially in close games where one pitch can decide the result. Either way, the KBO's experience has given every other league real evidence to learn from, rather than guesses about how an automated zone would play out over a full season.
Broadcasts adapted as well. Because every call comes from the same tracking data, television graphics showing the zone now match the call on the field, so viewers at home see exactly why a pitch was a ball or a strike.
For Baseball Dream players
In Baseball Dream's game engine, every pitch is also judged by the system against a fixed standard. Understanding the zone helps you choose pitchers: those with good control who work the corners tend to thrive under a consistent zone, and patient hitters can steadily pile up walks and time on base.