ABS challenge rules explained: How the MLB Automated Ball-Strike Challenge System works

A new challenge system has been introduced to Major League Baseball during Spring Training this season, after being tested over a number of years in the Minor League game.

Using Hawk-Eye ball-tracking technology, the Automated Ball-Strike (ABS) Challenge System will allow MLB players to contest human umpires’ decisions when a pitch is called as either a strike or a ball.

The introduction of the ABS Challenge System, which is similar to the technology that’s already used to challenge line calls in top-level tennis, was approved by MLB’s Joint Competition Committee in 2025.

How will the MLB challenge system work?

Teams will begin each game with two opportunities to challenge a human umpire’s ball-strike decision in the 2026 MLB season.

Only the batter, the pitcher or the catcher will be able to launch the challenge. The player signals his intention to challenge the umpire’s call by tapping his cap or helmet.

The pitcher, catcher or batter must tap his hat or helmet to let the umpire know they want to challenge the pitch.

If the team that sends a call to ABS is successful, it keeps its two challenges. If the umpire’s call is upheld, the team loses a challenge. Teams are given an extra challenge in each additional innings beyond the regulation nine.

Strike or ball?

MLB’s Hawk-Eye technology, which uses a reported 12 cameras to track a pitch’s trajectory, determines whether the delivery was thrown within the batter’s strike zone.

According to MLB, the strike zone is a 17-inch-wide, square area located over home plate. Vertically, it runs “from the midpoint between a batter’s shoulders and the top of the uniform pants […] and a point just below the kneecap”.

To qualify as a strike, a pitch’s trajectory must take it inside the strike zone, unless the batter swings at the delivery. To be counted as a ball, the pitch must be outside the strike zone.

Robo-ump rejected

As well as being tried out in Spring Training and Minor League Baseball, the ABS Challenge system was also tested out in the 2025 MLB All-Star Game in July, 2025.

In Minor League play, a full ABS system was also trialled, eliminating human umpires’ involvement in ball-strike calls. However, MLB said fans, players and managers showed a “clear preference” for the challenge system.

“Fans and baseball people still desire a human element of umpiring that involves feel for the game”, MLB said.

“A good thing”

Speaking to TMZ Sport, the three-time All-Star Jimmy Rollins offered his endorsement of the ABS Challenge System. “I think it’s a good thing - especially in big situations,” said Rollins, 46, who was a World Series winner with the Philadelphia Phillies in 2008.

“The game is trying to get better that way, because you should get rewarded for either taking a ball that’s a ball, or making a pitch that’s a strike.”

And Rollins insisted that the introduction of the new challenge system does not represent a step towards the complete replacement of human umpires in MLB. “That’ll never happen,” he declared.

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