How Major League Baseball players can turn to a robot to challenge balls, strikes this year

Robot umpires ar coming to the swelled leagues this year.

The Automated Ball-Strike (ABS) Challenge System will be introduced in the form of a challenge system in which the home plate umpire makes each call, with teams able to appeal to a computer system.

Robot umpires have been tested in the minor leagues since 2019, with recent trials at Triple-A since 2022, during MLB spring training last year and at the 2025 All-Star Game in Atlanta.

Here's what to know about MLB's robot umpires.

Stadiums are outfitted with cameras that track each pitch and determine whether it crossed home plate within the strike zone. In early testing, umpires wore earpieces and heard "ball" or "strike," then relayed the call to players and fans with traditional hand signals.

The challenge system adds a wrinkle. Human umpires call every pitch, but each team can challenge two calls per game. Teams that lose both challenges get one additional challenge in each extra inning. A team keeps its challenge if the appeal is successful, similar to video review rules in the major leagues, which were first used for home run calls in August 2008 and expanded to a wider range of plays for the 2014 season.

Only the batter, pitcher or catcher may challenge a call, signalling with the tap of a helmet or cap. Help from the dugout is not allowed. A challenge must be made within two seconds, and a graphic of the pitch and strike zone is shown on the scoreboard and broadcast feed. The umpire then announces the updated count.

Challenges during spring training last year averaged 13.8 seconds.

A Hawk-Eye pose-tracking system of cameras tracks pitches and determines whether they fall within a strike zone based on the each batter's height, measured without shoes. Each player will be measured for his strike zone between 10 a.m. And noon on a rolling basis during spring training to maintain consistency, because height can shrink later in the day. The data will be verified by the Southwest Research Institute. MLB estimated the calibration process at less than one minute for each player.

While the strike zone called by major league umpires tends to be oval-shaped, the ABS strike zone is a rectangle, as in the rule book.

Defining a computer-generated strike zone was one of the main challenges in developing the system.

MLB has changed the shape of the ABS strike zone several times.

It began with a width of 19 inches in 2022, then reduced to 17 inches, matching the width of home plate. Narrowing the zone led to more walks and only small changes in strikeout rates.

The top of the strike zone was set at 51 per cent of a batter's height in 2022 and 2023, then raised to 53.5 per cent in 2024 after pitchers complained. The bottom of the strike zone has been 27 per cent since 2022, after initially being set at 28 per cent. A batter's stance is not taken into account.

ABS makes its ball-or-strike decision at the midpoint of the plate — 8½ inches from the front and the back. That differs from the rule-book zone called by umpires, which treats the strike zone as a cube and defines a strike as any pitch that crosses any part of it. Major league umpires call roughly 94 per cent of pitches correctly, according to UmpScorecards.

ABS, which utilizes Hawk-Eye cameras, has been tested in the minor leagues since 2019. The independent Atlantic League trialed the system at its 2019 All-Star Game, and MLB installed the technology for that year's Arizona Fall League featuring top prospects. ABS was used at eight of nine ballparks in the Low-A Southeast League in 2021, then moved up to Triple-A in 2022.

At the start of the 2023 Triple-A season, half the games used robot umpires for ball-strike calls, while the other half had a human umpire making calls that could be appealed to ABS.

MLB switched Triple-A to an all-challenge system on June 26, 2024, then used the challenge system last year at 13 spring training ballparks hosting 19 teams for a total of 288 exhibition games. Teams won 52.2 per cent of their ball-strike challenges, succeeding on 617 of 1,182 appeals.

At last year's MLB All-Star Game, four of five challenges to plate umpire Dan Iassogna's calls were successful.

Success rate have hovered around 50 per cent in the minors.

At Triple-A last season, the success rate dropped to 49.5 per cent from 50.6 per cent. Defences —usually catchers — were more successful, winning 53.7 per cent of challenges compared with 45 per cent for batters. Challenges also rose to 4.2 per game from 3.9.

In 2024 at Triple-A, just 1.6 per cent of first pitches were challenged. That rose to 3.9 per cent for two-strike pitches, 5.2 per cent for three-ball pitches and 8.2 per cent for full counts.

Challenge rates were also higher later in games. While 1.9 per cent of pitches were challenged in the first three innings, that rose to 2.5 per cent from the fourth through sixth, 2.8 per cent in the seventh and eighth and 3.6 per cent in the ninth.

---

---