MLB's New ABS Challenge System Exposes Worst Umpire CB Bucknor

Controversial umpire's calls overturned at record rate as new robot umpire technology highlights his inaccuracy.

Apr. 2, 2026 at 7:50pm by Ben Kaplan

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A cubist, geometric painting depicting a baseball umpire making a call at home plate, the scene fractured and abstracted into overlapping planes of color and shape, conveying the disruption and controversy surrounding umpiring in the modern game.The ABS Challenge System is deconstructing the traditional role of the baseball umpire, exposing long-standing issues with inconsistent and inaccurate officiating.San Francisco Today

MLB's new Automated Ball-Strike (ABS) Challenge System, which allows players to challenge umpire calls on balls and strikes, has exposed umpire CB Bucknor as the least accurate in the league over the past five years. During a recent game between the Rays and Brewers, Bucknor had a league-high 78% of his calls overturned by the robot umpire, far exceeding the league average of 55%. This comes after a disastrous outing where he made a blatantly incorrect call on a play at first base, drawing laughter from both teams' managers.

Why it matters

The ABS Challenge System is shining a light on the inconsistencies and inaccuracies of human umpires, with Bucknor emerging as one of the worst offenders. As the technology becomes more prevalent, umpires who have relied on a more subjective strike zone will struggle to adapt, potentially leading to increased scrutiny and accountability for their performance.

The details

During a recent game between the Tampa Bay Rays and Milwaukee Brewers, umpire CB Bucknor took a foul ball to the mask and had to be helped off the field, capping off a particularly bad week for the controversial official. Earlier in the week, Bucknor had several of his calls overturned by the new ABS Challenge System, with Eugenio Suarez of the Reds successfully challenging back-to-back strike three calls. Overall, Bucknor had 6 of 8 challenges overturned, with the two calls that stood being extremely close to the strike zone edge. Bucknor's misses were more dramatic, with three pitches he called strikes missing the zone by 2.4 inches or more, including one that was 2.7 inches outside.

  • On Saturday, Eugenio Suarez successfully challenged two of Bucknor's strike three calls.
  • During Wednesday's Rays-Brewers game, Bucknor took a foul ball to the mask and had to be helped off the field.

The players

CB Bucknor

A veteran MLB umpire who has been rated as the least accurate umpire in the league over the past five years, with his calls being overturned at a league-high rate of 78% since the introduction of the ABS Challenge System.

Eugenio Suarez

A player for the Cincinnati Reds who successfully challenged two of Bucknor's strike three calls during a recent game, drawing loud cheers from the crowd.

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What they’re saying

“It doesn't matter that Suarez ultimately grounded out. What matters is that, in a game where the Reds hit two home runs, the loudest cheers came for a pair of successful ABS challenges.”

— Terrence O'Brien, Author

What’s next

As the ABS Challenge System becomes more widely adopted, umpires like CB Bucknor who have relied on a more subjective strike zone will need to adapt to the more consistent and mathematical approach of the robot umpire. This could lead to increased scrutiny and accountability for umpire performance across the league.

The takeaway

The introduction of the ABS Challenge System has exposed the inconsistencies and inaccuracies of human umpires, with CB Bucknor emerging as one of the worst offenders. This technology is shining a light on the need for more objective and consistent strike zone enforcement in Major League Baseball.