MLB unveils ABS challenge system guidelines for 2026 season

"If a team enters extra innings without a challenge, they'll be given an extra one every inning. The challenges will not accumulate if not used. Teams will never have more than one challenge per extra inning unless they entered extra frames with their original two intact. It's possible for both an ABS challenge and video replay challenge to occur on the same play. If that happens, the ball-strike call will be adjudicated first, followed by the video replay on the bases."

"Umpires will be given discretion on plays that happen on the bases, even when a pitch is being challenged. For example, the outcome of a stolen base attempt is likely to stand no matter the outcome of the challenge, with the lone exception coming on a ball-four or strike-three call that is overturned. If the umpire deems "player behavior" has been impacted -- for example, if the catcher stops playing because he hears ball four and the call is overturned -- he might send the runner back to his original base and the stolen base won't count."

"A pitch may not be challenged if a position player is pitching. The league is measuring the standing height of each player to determine their individual strike zone, which will be slightly smaller than the umpire called zone. Also Thursday, the league announced a tweak to its obstruction rule: A runner who initiates contact with a fielder with the intent to draw an obstruction call will be called out."

Major League Baseball finalized the automated ball-strike (ABS) challenge system rules for its Opening Day debut. Teams entering extra innings without a challenge will receive one extra challenge each inning, though extra-inning challenges do not accumulate and teams cannot have more than one per extra inning unless they retained their original two. Umpires retain discretion on base plays during pitch challenges and can restore or reverse base outcomes if player behavior is affected. Position players pitching cannot have pitches challenged. Standing height measurements will define individual strike zones slightly smaller than umpire-called zones. ABS and video replay challenges can occur on the same play, with ball-strike adjudicated first.

Read at ESPN.com