SCOTTSDALE, Ariz. — Major League Baseball is changing … again.
Amid an era that has already seen significant alterations to the sport, most of which have been received favorably by fans and players alike, MLB will introduce perhaps its most dramatic change yet in 2026: the ability to challenge ball and strike calls.
For the past four seasons, MLB has invested heavily in testing the use of Automated Ball Strike (ABS) technology, predominantly at the Triple-A level but also during 2025 major-league spring training and the 2025 All-Star Game. At the minor-league level, early experimentation included the use of ABS to call all balls and strikes based on a designated virtual strike zone — crafted in space using 12 Hawk-Eye cameras placed around the perimeter of the field and tracking the pitch’s location, with the top and bottom boundaries of the zone determined by the batter’s height — with calls communicated to the home plate umpire via earpiece. But feedback on such a comprehensive system was less than positive among fans and players.
Instead, there was quickly a consensus among all parties that ABS would be better deployed in a limited capacity. Rather than completely eliminating the home plate umpire’s perspective, ABS — which offers a more black-and-white interpretation of the strike zone than a human ever could — could act as more of a support system than an overarching rule of law. Indeed, starting this season, no longer will MLB players have to begrudgingly accept a home plate umpire’s ruling no matter what; modern technology has provided the chance for recourse.
In September, the Joint Competition Committee — a group of six owners, four active players and one active umpire — voted to introduce the ABS challenge system for the 2026 season. On Thursday, at the conclusion of the annual Cactus League media day, former big-league pitcher and current vice president of on-field strategy for MLB Joe Martinez gave a presentation on how the ABS challenge system will function in 2026. It was similar to the one MLB gave a year ago ahead of its first round of testing in big-league spring training games, but this time, the stakes are considerably higher. This is no longer some early-stage experiment. This system is coming on Opening Day.
Welcome to a world in which players canargue balls and strikes — at least some of the time. In reintroducing the concept of the ABS challenge system, MLB stated its objective early and emphatically: “To provide players with an opportunity to correct missed calls in high-leverage moments in a manner that fans like.”
Here are the basics of how the ABS challenge system will work:
Each team will have two challenges to begin each game, and all successful challenges will be retained.
Only the batter, catcher and pitcher are allowed to challenge a ball or strike call; protests from the bench or elsewhere on the field are prohibited, and umpires have the ability to deny a challenge if they believe it was aided or influenced by anyone else on field or in the dugout.
To challenge a call, the pitcher, catcher or batter must tap his head immediately (in less than two seconds, roughly) to initiate a review. At that point, the umpire will announce the call is being challenged, and a graphic showing the ball’s location as determined by ABS will be displayed on the scoreboard and broadcast. The result of the challenge will be announced, and play continues. (In the past, even before ABS was a factor, there have sometimes been minor discrepancies between the strike zone displayed on the broadcast, the one embedded in MLB’s Gameday app and the one appearing on Baseball Savant’s Gamefeeds. MLB is working to ensure that all available forms of the strike zone are reflective of the zone being used by the ABS challenge system.)
MLB defines the strike zone as “a two-dimensional rectangle that is set in the middle of home plate with the edges of the zone set to the width of home plate (17 inches) and the top and bottom adjusted based on each individual player’s height (53.5% of the batter’s height at the top and 27% at the bottom).” If any part of the ball is touching that strike zone — as tracked by the Hawk-Eye cameras — it is considered a strike.
Because the system is based entirely on player height, MLB has arranged for independent testers to measure all players during spring training using a standardized process to ensure that no player’s zone is too large or small based on a misreported height.
If a game goes to extra innings, each team will be awarded one extra challenge each inning, but only if they do not have any remaining. For example, a team that has two challenges left after nine innings would not gain a third challenge for the 10th, but a team with zero challenges remaining after nine innings would regain one challenge for the 10th. This repeats with each successive extra inning.
Challenges cannot be used if a position player is pitching.
On Thursday, MLB also supplied some data regarding how challenges came into play during spring training last year and another full season of testing in Triple-A. The overturn rate in Triple-A in 2025 was 50%, while the rate in spring training was 52%. Interestingly, catchers (56% overturn rate) were notably more successful at overturning calls than batters (50%) or pitchers (41%), lending credence to the possibility that some teams will institute strict guidelines regarding which of their players have the latitude to challenge calls. That’s just one of several strategic elements of the ABS challenge system that are still being contemplated by front offices, coaches and players in camp.
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Another data point that could illuminate potential strategy is when during games the challenges have most commonly been deployed. In Triple-A, challenges were far more frequent in the later innings than the early innings, perhaps a reflection of a strategic preference to save challenges for more consequential or higher-leverage moments later in a game.
Conversely, in big-league spring training last year, the bulk of the challenges were used earlier in games, often in the first three-to-five innings. But as Martinez pointed out, that likely had less to do with a conscious strategy and more with who was playing earlier in those games: veterans testing the system before they exited to make way for the prospects and minor leaguers who often occupy the later innings of Cactus and Grapefruit League contests. This dynamic is crucial to keep in mind as we prepare for another spring with the ABS challenge system in action.
Before we get to Opening Day, this spring will provide a larger sample of data for us to glean a preview of what’s to come. Last year, Hawk-Eye was installed in a select number of spring training ballparks, thus limiting certain teams’ exposure to the system; this time around, Hawk-Eye is in every spring training ballpark. But while teams are now preparing behind the scenes for how to take advantage of the challenge system in games that count, it’s unlikely that will meaningfully change their behavior — or that they’ll reveal such strategies — in exhibition contests.
Further complicating matters is the high percentage of players who will depart spring training early to participate in the World Baseball Classic — in which the ABS challenge system will not be used — and thus miss out on the reps with the system leading up to its official introduction in the regular season.
All of this adds to the intrigue surrounding a new technology that will transform the sport in myriad ways we are still in the earliest stages of fully grasping. A spring training with widespread use of the ABS challenge system will serve as an appetizer to this new world we’re about to enter.
But we won’t know the full scope until the real games commence at the end of March. Opening Day can’t get here soon enough. Let the head tapping begin.