Baseball's Robot Umpires Explained: How the ABS Challenge System Works

01 / The story

What changed in 2026

In September 2025, MLB's Joint Competition Committee voted to bring the Automated Ball-Strike Challenge System to the major leagues for the 2026 season, after years of testing in the Minor Leagues and use during 2025 Spring Training and the 2025 All-Star Game. The system is sponsored as 'powered by T-Mobile.' [1, 2]

This is a challenge system, not full automation. A human home-plate umpire still calls every ball and strike. Technology enters only when a player disputes a call—and only a limited number of times per game.

This guide reflects MLB's published explanations of the system, checked on October 17, 2026. Rules can be adjusted between seasons, so check MLB's current documentation for the latest details. Source numbers refer to the direct links after the FAQs.

02 / The story

How a challenge works

Each team starts the game with two challenges. A successful challenge is kept; a failed one is lost. Only the pitcher, catcher or batter involved in the pitch can initiate a challenge, and the request must come immediately after the pitch—signaled by tapping the hat or helmet. Help from the dugout or other players is not allowed. [1]

Once a challenge is signaled, the Hawk-Eye tracking system's view of the pitch is shown on the stadium video board and broadcasts. The graphic shows whether any part of the ball passed through the strike zone, and the call is confirmed or overturned. The whole process takes roughly a few seconds—fast enough that the game barely pauses.

The design deliberately puts the decision in players' hands. Catchers, who see hundreds of pitches up close, have proven especially central to challenge strategy in testing.

03 / The story

The technology: Hawk-Eye cameras

ABS runs on Hawk-Eye, a high-speed camera system long known from professional tennis line-calling. A network of cameras around the ballpark tracks the ball's trajectory from the pitcher's hand to the catcher's glove, building a precise three-dimensional path for every pitch. [3]

The strike zone is defined as a three-dimensional volume over home plate, with its top and bottom adjusted to each batter's stance. The system checks whether the ball's path intersected that volume. This is geometry from camera measurements—not an AI guessing what 'looks like' a strike.

Hawk-Eye has powered MLB's Statcast tracking since 2020, so the 2026 change built on cameras already installed in every ballpark rather than introducing entirely new hardware. [3]

04 / The story

Why a challenge system instead of full robot umpires

MLB describes the challenge system as a middle ground. A fully automated system would call every pitch by camera, removing the human umpire's judgment entirely. The challenge approach keeps the traditional rhythm of the game while correcting the small number of calls that matter most—and that players feel most strongly about. [1]

The human baseline is already high: big-league umpires call roughly 94 percent of pitches correctly, according to UmpScorecards, an independent tracker cited by MLB. The challenge system targets the remaining few percent without redesigning the sport. [1]

Testing in the minors and in 2025 spring training showed games stayed fast and players adapted quickly—evidence that helped convince the competition committee to approve the change.

05 / The story

Accuracy, limits and fairness questions

No measurement system is perfect. Hawk-Eye's tracking is extremely precise, but the strike zone's edges depend on each batter's measured stance, and any system has a margin of error. The challenge graphic presents a definitive verdict; the underlying measurement is a very good estimate.

Fairness debates continue. Some argue a camera-defined zone is more consistent than any human; others note that framing skill—how catchers present a pitch—loses value, and that teams with savvier challenge strategies gain an edge. The two-challenge limit also means some wrong calls will stand simply because challenges ran out.

One misconception to avoid: the system does not eject umpires or overrule them automatically. Umpires remain in charge of the game; ABS is a review tool, like instant replay for the strike zone.

06 / The story

What could come next

If the challenge system runs smoothly, MLB could adjust the number of challenges or expand automation in future seasons. A fully automated strike zone remains technically possible—the cameras already track every pitch—but the league has publicly favored the challenge model, and any change would need competition-committee approval. Treat predictions about full robot umpires as possibilities, not plans. [2]

For fans, the practical change is simple: expect a few dramatic hat-taps per game, a quick video-board verdict, and fewer arguments that change nothing. The human umpire is still there—the robots just got a appeal process.