MLB ABS Challenge System Explained: How Automated Ball-Strike Challenges Work in Baseball

Mar 25, 2026 - 13:30

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Detailed view of the scoreboard showing an ABS ball and strike challenge call being overturned during the Los Angeles Dodgers against the Arizona Diamondbacks during a spring training game at Camelback Ranch-Glendale.

MLB ABS Challenge System Explained: How Automated Ball-Strike Challenges Work in Baseball originally appeared on NESN. Add NESN as a Preferred Source by clicking here.

If you are watching a game and suddenly see a batter, catcher or pitcher tap their helmet after a borderline pitch, that is MLB’s ABS challenge system in action. “ABS” stands for Automated Ball-Strike system, but in the majors it does not mean full-time robot umpires calling every pitch. Instead, the plate umpire still makes the original call, and players can challenge certain ball-or-strike calls for a near-instant review. MLB approved the system for Major League play beginning in 2026, and it is now used in spring training, the regular season and the postseason.

What is the ABS challenge system?

Detailed view of the scoreboard showing an ABS ball and strike challenge call being overturned to a strikeout during the Chicago White Sox against the Chicago Cubs during a spring training game at Camelback Ranch-Glendale.

Mark J. Rebilas-Imagn Images

The simplest way to think about it is this: MLB kept the human umpire, then added a limited challenge system for obvious misses. If a pitcher, catcher or batter thinks the umpire got a ball-or-strike call wrong, that player can challenge it immediately. A Hawk-Eye camera system tracks the pitch, compares it to the batter’s assigned strike zone, and the result is shown on the scoreboard and broadcast. The review takes about 15 seconds.

That means ABS in MLB is not the same thing as fully automated strike calls on every pitch. The umpire still calls the game pitch by pitch. The technology only steps in when a player on the field uses one of the team’s challenges.

How ABS challenges work during a game

Here are the rules fans need to know:

Each team starts with two challenges in a nine-inning game.
A team keeps its challenge if the call is overturned, and loses it if the umpire’s original call stands.
Only the pitcher, catcher or batter can initiate a challenge. Managers and dugouts cannot.
The player must challenge immediately after the pitch by tapping their hat or helmet and vocalizing the challenge.
In extra innings, a team that enters the inning with no challenges left gets one new challenge.
MLB’s Statcast ABS dashboard says challenges are not permitted when a position player is pitching.

That immediately part matters. Players are supposed to make the decision themselves, without waiting for help from the dugout, teammates or coaches. MLB even adjusted some broadcast graphics so teams cannot easily relay pitch-location help from the bench.

How the strike zone is measured

Detailed view of the scoreboard during an ABS ball and strike challenge by the Los Angeles Dodgers against the Chicago White Sox during a spring training game at Camelback Ranch-Glendale. The umpires call would be overturned.

Mark J. Rebilas-Imagn Images

MLB’s challenge zone is a two-dimensional rectangle, not the old TV-style fuzzy box and not a full three-dimensional cube. It is set over the middle of home plate, not the front edge. The zone is 17 inches wide, matching the width of the plate. The top is set at 53.5% of the batter’s measured height without cleats, and the bottom is set at 27% of that height. Any part of the baseball touching any part of the zone counts as a strike.

MLB settled on that version after years of testing. The league found that a three-dimensional zone or a zone judged at the very front of the plate could produce weird-looking strike calls on breaking balls that clipped the zone early and then bounced far away from where hitters or fans expected.

One other important detail: the ABS zone is based on a player’s measured height, not the exact crouch or stance he uses in that plate appearance. So a hitter who squats lower may feel like the top and bottom of the zone are not where he is used to seeing them.

Does ABS actually change a lot of calls?

Less than you might think, which is part of the point. In MLB’s 2026 spring testing, only 1.4% of all pitches were challenged, and only 7% of edge-zone takes were challenged. The overturn rate was 53%, with batters succeeding 45% of the time and fielding teams succeeding 60% of the time. MLB also found that 65% of spring games had two or fewer overturned calls.

So ABS is not turning every game into a replay fest. It is more like a pressure-release valve for the most important close calls.

That is also why MLB likes this setup: it adds accuracy without stripping away the human part of calling a game. And it could reduce some of the sport’s most familiar arguments. MLB noted that 63.2% of ejections in 2025 were about balls and strikes, so the challenge system gives players a way to contest calls without immediately turning the moment into a shouting match.

The easiest takeaway for fans is this: when you see an ABS challenge, you are watching baseball’s version of a quick correction tool. The umpire still has the plate. The players just have a limited chance to say, Check that one.