MLB challenge system, explained: What to know about ABS and robot umpires in 2026 season

Another major change is coming to MLB.

Just years after the ghost runner and pitch clock rules significantly changed the rhythm of baseball, shortening game length, the league is now addressing a different issue: missed calls. Specifically when it comes to balls and strikes, umpires will have a closer eye on them starting in 2026.

That's because "robot umpires," in a sense, have officially arrived to MLB. The human element remains, but players will now instantly be able to challenge balls and strikes virtually whenever they desire — which will be most consequential in a game's biggest moments.

Here's a full breakdown of the ABS system coming to MLB in 2026.

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What is ABS in baseball?

ABS is the new technological challenge system coming to MLB in 2026 that allows pitches, and whether they were a ball or strike, to be decided upon using Hawk-Eye cameras at the ballparks.

In essence, ABS is a "robot umpire." However, it is not MLB's full-time umpiring system — it is only being used for challenged calls, and teams will have limited amounts of challenges available.

What does ABS stand for?

ABS stands for "Automatic Ball-Strike." The system, after being previously tested in the Minor Leagues for years and in 2025 Spring Training, is being fully implemented for MLB games in the 2026 season.

The ABS system and the cameras required to monitor each pitch is being added to every MLB stadium — but for games like the Mexico City Series or the Field of Dreams game, it will not be available.

Each pitch is tracked by the system, relative to the batter's strike zone. 

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ABS rules for 2026

The ABS system is not replacing human umpires, but rather adding a "backup" component and some strategy to how teams use their challenges. 

Here's a guide to the ABS rules for the 2026 MLB season.

Who can challenge pitches?

Not every player on the field is allowed to challenge a ball/strike call. That capability lies only in the hands of the batter, pitcher and catcher at the time of the pitch.

Managers are not able to challenge a pitch call. And decisions to challenge must be instantaneous — meaning a pitcher, batter or catcher does not have time to confer with their manager or coaches before deciding to challenge.

Umpires are also allowed to disallow a challenge if they decide the challenging player was aided by other players, the dugout or runners. Challenges are intended to be a player-only decision; requested challenges can also be denied for taking too long.

A level of strategy is certainly involved; some teams have shared that they will only grant the challenging ability to their catchers and batters, preferring pitchers don't get involved. But at the end of the day, there are only three players who can make that choice, and they're all part of the original play.  

How many challenges do teams get per game?

Each team starts the game with two challenges. However, if the game goes to extra innings, any team that is out of challenges will receive one per inning. If a team still has a challenge remaining for extra innings, then it does not receive a second challenge.

For each extra inning, each team will have one challenge available.

Successful challenges are retained — meaning that a team only loses its challenge if the umpire's original call was confirmed. Because challenges are limited, teams will have some strategy involved in "saving" them.

When position players are pitching, challenges are not allowed.

The Braves' win today ended on a successful ABS challenge, powered by @TMobile. pic.twitter.com/ezDqhZnByB

How are challenges issued?

To use a challenge, a player must tap their helmet/hat to signal to the umpire that they would like to challenge the call. Players are also encouraged to verbally tell the umpire they are challenging, to avoid confusion.

Challenges are to be used in the immediate moments after a pitch, either within the following seconds, or if there is a play after the pitch, after that play is over.

Will ABS be used in the postseason?

Yes, the Automatic Ball-Strike system will be used in the postseason.

It will apply to all MLB games moving forward, outside of games held at stadiums that aren't the home of one of the 30 teams, such as the Field of Dreams game.

How is each player’s automated strike zone determined?

The strike zone for the ABS system is determined on a batter-by-batter basis, which is no different than how a human umpire would judge the strike zone. However, there is more math involved, and a player's height matters.

Per MLB.com, in spring training, every position player had their heights measured without cleats by "a team of independent testers conducting manual measurements," and by representatives from "a research institute using biomechanical analysis to confirm the manual measurements and safeguard against potential manipulation."

Those heights are then used to determine the player's ABS strike zone.

The ABS strike zone is 17 inches wide, the same as home plate. The top end of the zone is the equivalent to 53.5% of the player's height, while the bottom end is equivalent to 27% of the player's height. The depth of the zone is 8.5 inches from both the front and back of the plate to its center.

Will the strike zone box on TV still show strikes?

It depends on which TV broadcast, as its up to the broadcasters. However, with the ABS system in-place, MLB has requested broadcasters to no longer differentiate a circle in the box to indicate whether a pitch was a ball or a strike.

The on-screen strike zone box may remain, but viewers won't get the same instant "ball" or "strike" indicators from the broadcast. Because of that, there won't be as much instant feedback for fans as to whether a close pitch was a ball or strike, unless the ABS system is used.

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