From the Atlantic League to the Big Leagues
The technology didn't start in the majors
The technology behind Major League Baseball's Automated Ball-Strike system didn't originate in the big leagues; its earliest roots were planted in the independent Atlantic League back in 2019. In those early experimental days, the system operated as a full robot umpire. A radar device tracked the pitch and directly transmitted every single ball or strike call into an earpiece worn by the home plate umpire, who then relayed the robotic decision to the field. It provided a welcomed sense of consistency for players, eliminating the frustration of adjusting to a different human umpire's subjective strike zone every single night.
However, when MLB fully implemented the technology for the 2026 season, they pivoted from the fully automated model to a strategic Challenge System.
The Mechanics of the Challenge System
Humans still call the game — the machine is the safety net
Under the current MLB rules, the human umpire still calls the balls and strikes on the field in real time. But now, the high-tech sensors and optical tracking cameras serve as a safety net. Each team is allotted a total of two appeals per game. A review is instantly triggered by a player tapping their helmet within a tight two-second timeframe following the pitch. Only the batter, pitcher, and catcher have the authority to appeal. If a team is out of challenges as the game progresses into extra innings, they are granted one extra appeal for that inning.
When an appeal is initiated, the system runs through a rapid process utilizing Hawk-Eye optical cameras. This data is instantly adapted into a 2D layout displayed on the main video screen in the stadium, allowing the entire audience to react to the digital verdict in real time. If the appeal successfully overturns the human umpire's call, the team retains their challenge; if it fails, they lose it.
The Data: Who Challenges Best?
Players trust their instincts — and the numbers back them up
This dynamic has made a significant impact on the pace and strategy of the game. Pitchers rarely initiate these appeals themselves; most of the time, they defer to the catcher's judgment. As the data shows, players have been remarkably accurate when they choose to stop the game.
The average game features about four total appeals. A record of 12 appeals was set during a game between the Oakland Athletics and the St. Louis Cardinals, and remarkably, nine of those human calls were overturned. This proves that the players acting on instinct are highly reliable at judging the strike zone.
Combined across both teams, with usage climbing steadily as games move into the later innings.
7 from Oakland, 5 from St. Louis, and 9 of the 12 were overturned — the busiest and most accurate high-volume challenge game of the season.
The Death of the Frame Job — and High-Leverage Strategy
Where and when teams actually spend their challenges
In the past, a catcher would often move their glove up to trick the umpire into misjudging where the pitch was located. With the ABS system acting as the ultimate judge during an appeal, that framing technique is rendered useless on challenged pitches. The system relies on a rigid 17-inch wide strike zone. However, since teams only have two appeals to burn, catchers can still attempt to slip their framing routines in on non-appealed pitches to steal a strike.
Interestingly, 54 percent of challenged calls are made late in the game, specifically after the 6th inning. Furthermore, the highest usage occurs in high-leverage situations like extra innings. The full-count pitching scenario is the most common trigger; when a player is at a 3-2 count, they are most willing to risk burning an ABS appeal. Location data also shows that the bottom border of the strike zone is where appeals are used the most, followed closely by the top border. This stands in stark contrast to the inside pitch, which is the least appealed location on the plate.