MLB Introduces Computer-Assisted Strike Calls This Season

Major League Baseball will implement its Automated Ball/Strike System this year, allowing teams to challenge umpire calls using computer technology. The system uses camera technology to track pitches and has been tested in minor leagues since 2019.

Major League Baseball will debut computer-assisted umpiring technology this season, marking a significant shift in how ball and strike calls are made.

The league’s Automated Ball/Strike System operates as a challenge-based format where traditional umpires continue making initial calls, but teams can appeal decisions to computer verification. This technology has undergone extensive evaluation in minor league play beginning in 2019, with comprehensive testing at Triple-A level starting in 2022, during MLB spring training last season, and at the 2025 All-Star Game in Atlanta.

The system relies on strategically positioned cameras throughout ballparks that monitor every pitch and determine whether it passes through the strike zone over home plate. During initial trials, umpires received audio feedback through earpieces announcing “ball” or “strike,” then communicated these decisions using standard gestures.

Under the challenge format, human officials make all initial pitch calls, but each team receives two opportunities per game to contest decisions. Teams losing their challenges earn one additional appeal during each extra inning. Successful challenges allow teams to keep their remaining appeals, mirroring current video review procedures that began with home run calls in August 2008 and expanded significantly for the 2014 season.

Challenge requests can only come from batters, pitchers, or catchers, who signal by tapping their helmet or cap, with dugout assistance prohibited. Appeals must occur within 2 seconds, after which the pitch trajectory and strike zone graphic appears on scoreboards and television broadcasts. Umpires then announce any count changes.

Last year’s spring training challenges required an average of 13.8 seconds to resolve.

The Hawk-Eye pose-tracking camera system monitors pitches and compares them against individualized strike zones based on each batter’s height, measured without footwear. Players undergo strike zone measurements between 10 a.m. and noon on a rotating schedule during spring training, with this specific timeframe chosen for consistency since height decreases throughout the day. The Southwest Research Institute validates all measurements, with MLB estimating under one minute per player for the calibration process.

While traditional umpire strike zones tend to form oval shapes, the ABS creates rectangular zones matching official rulebook specifications.

Establishing the computer strike zone parameters required extensive deliberation.

MLB has modified the ABS strike zone dimensions multiple times.

The system began with 19-inch width in 2022, then reduced to 17 inches to match home plate dimensions. This narrower zone increased walk rates while producing minimal strikeout changes.

The upper strike zone boundary was set at 51% of batter height in 2022 and 2023, then increased to 53.5% in 2024 following pitcher complaints. The lower boundary has remained at 27% since 2022, down from an initial 28%. Batter positioning doesn’t influence these calculations.

ABS evaluates pitches at the plate’s center point, 8.5 inches from both front and back edges. This differs from the rulebook zone used by umpires, which defines the zone as three-dimensional with strikes occurring when any portion crosses through. Current big league umpires achieve approximately 94% accuracy on pitch calls, according to UmpScorecards data.

The Hawk-Eye camera-based ABS has undergone minor league testing since 2019. The independent Atlantic League first trialed the technology during its 2019 All-Star Game, followed by MLB installation for that year’s Arizona Fall League featuring top prospects. Eight of nine Low-A Southeast League ballparks used ABS in 2021, before advancing to Triple-A in 2022.

Triple-A began the 2023 season with half their games using automated ball/strike calls and half employing human umpires subject to team appeals.

MLB converted all Triple-A games to the challenge system on June 26, 2024, then implemented it across 13 spring training facilities hosting 19 teams for 288 exhibition games last year. Teams successfully overturned 52.2% of their ball/strike challenges (617 of 1,182 attempts).

During last year’s MLB All-Star Game, four of five challenges against plate umpire Dan Iassogna’s calls succeeded.

Minor league success rates have consistently hovered near 50%. Triple-A’s success rate decreased to 49.5% from 50.6% last season. Defensive players, primarily catchers, achieved better results with 53.7% successful challenges compared to 45% for batters. Challenge frequency increased from 3.9 to 4.2 per game.

In 2024 Triple-A play, only 1.6% of first pitches faced challenges, but rates climbed to 3.9% on two-strike counts, 5.2% on three-ball counts, and 8.2% during full counts.

Challenge rates increased as games progressed. The first three innings saw 1.9% of pitches challenged, rising to 2.5% from the fourth through sixth innings, 2.8% in the seventh and eighth, and 3.6% in the ninth inning.