The MLB officially implemented the Automated Ball-Strike (ABS) Challenge System for the 2026 season debuting Opening Night.
The ABS Challenge System was tested and used during Spring Training and Special Events in 2025.
The announcement comes as a major development for the league and its future, and it could be the first step to the MLB implementing “robot umpires” – a topic that has lingered around the sport as more professional sports leagues turn to technology, rather than humans, to help officiate games.
So what is ABS, how does it work, and why is the MLB implementing it now?
We discuss all of that in this article.
What is the ABS challenge system?
The ABS challenge system is a way to review umpire ball and strike calls using technology.
The ABS challenge system does not mean balls and strikes will be called by a computer. Rather, a computer – in this case, “Hawk-Eye” technology – is consulted if a player challenges the ball or strike call made by the human umpire.
If any of the pitcher, catcher or batter involved in the play believes the umpire made an incorrect ball or strike call, they can tap their cap or helmet to signify they are challenging the call.
Then, the “Hawk-Eye view” of the pitch – the exact location of the pitch relative to the batter’s strike zone - is shown on the stadium video board and TV broadcast, and a final call is determined.
What is the difference between full ABS and the ABS challenge system?
Full ABS differs from the ABS challenge system as it removes the human umpire making ball and strike calls from behind home plate.
Full ABS, which was tested in Minor League Baseball, removes the element of umpire human error altogether, and ball and strike calls are exclusively determined by the Hawk-Eye technology.
While being tested in the minors, full ABS resulted in more walks, and thus, longer games, which contradicts other recent MLB rule changes such as the pitch clock. The system also negated pitch framing, a tactic used by pitchers and catchers for decades.
Overall, “fans, players, managers and other personnel” were in favor of the challenge system over full ABS, per the MLB.
ABS challenge system testing and history
So what spurned the MLB to introduce the ABS challenge system now, when umpire ball-strike calls have been a topic of debate for years?
Umpires have called balls and strikes for more than 160 years, with the first recorded evidence coming in 1864. Baseball players arguing ball and strike calls has become commonplace at all levels of the sport, leading to famous outbursts and meltdowns and huge points of controversy.
In the modern MLB, umpires who make incorrect ball and strike calls are under more scrutiny than ever. There are more eyes, cameras, angles, instant replays and metrics in the game now than ever, and fans, players and teams have wondered why the highest level of the sport still relies on the human eye to make calls that impact the outcome of games, particularly when other professional sports have adopted technology to help their officials.
Adding the ABS challenge system in 2026 comes off the back of sufficient testing during the 2025 Spring Training season and Triple-A seasons in 2023 and 2024, which is the highest level of Minor League Baseball.
Full ABS was first used in the independent Atlantic League in 2019, and the challenge system was first used in the Florida State League in 2022.
How was the ABS challenge system used in 2025 MLB Spring Training
During the 2025 Spring Training season, the ABS challenge system was used in 13 of 23 spring training ballparks. The system was not in place for every game at every park, but it allowed every team to experience the challenge system at some point during their spring training.
Key 2025 Spring Training ABS Findings:
There was an average of 4.1 challenges per game.
Each challenge took an average of 13.8 seconds, adding less than a minute per game.
Challenges resulted in a 50/50 overturn rate.
ABS challenge system rules
The ABS challenge system will follow the below rules in 2026 season:
Each team will have two challenges per game.
The batter, pitcher or catcher involved in the play can challenge the call by tapping their helmet or cap. Managers are not allowed to challenge.
If a challenge is successful, the team retains their challenge. If unsuccessful, the team loses that challenge.
If the game goes into extra innings, and a team has used all of its challenges gets one new challenge for every extra inning.
The ABS strike zone parameters are: 17 inches wide, 8.5 inches of depth (from front to back of home plate), the top end of the zone is 53.5% of the batter’s height, and the bottom end is 27% of the batter’s height.
