Underdog Stories / Sports analysis & explainers
How Does MLB’s ABS Challenge System Work?
How does MLB's ABS challenge system work? See who can ask for a review, when teams keep a challenge, and why one quick decision can change an at-bat.
By Brett Hanson · Underdog Podcasts · November 10, 2026
On an episode of Long Gone, Michael Dault described the gesture that can stop a baseball game: a player taps his head. The screen shows where the pitch crossed the plate. Seconds later, someone is pleased, and someone has lost an argument.
How does MLB’s ABS challenge system work? A human umpire calls every pitch. After a called ball or strike, the batter, pitcher, or catcher can promptly tap a cap or helmet to request an automated check. Each team starts with two challenges. A correct challenge stays available; an incorrect one is lost.
That sounds simple enough. The hard part is deciding when to trust your eyes.
How does the new ABS challenge system work in MLB?
ABS stands for Automated Ball-Strike. MLB began using its challenge version in regular-season games in 2026, after testing it in the minors and spring training. It was also used in the postseason.
The system tracks a pitch against the batter’s measured strike zone. It does not call every pitch aloud. The plate umpire still does that, just as before. ABS steps in only when an eligible player challenges a called ball or strike.
Then the ballpark video board and the broadcast show an animated view of the pitch. If ABS finds that the umpire’s call was wrong, the call changes. If the umpire was right, it stands. Play resumes after the result.
In episode “289: Mariners, What the Hell?”, Dault liked the speed of that reveal. He also worried about what it might mean for umpires over time. Those are separate questions. A fast check can fix one call without telling us what baseball might choose to do years from now.
For now, fans still hear an umpire call the pitch. Most of the time, that is the end of it.
Who can challenge a ball or strike?
Only the batter, pitcher, or catcher can start an ABS challenge. The manager can’t do it from the dugout, and a teammate in the field can’t signal for one either. The choice stays with the people involved in the pitch.
The player taps a cap or helmet, usually within roughly two seconds of the call. MLB also encourages players to say they are challenging. The tap is the official signal.
There is little time to consult anyone. If an umpire decides the player got help from the dugout or another player, the request can be denied. A late request can be denied too. In either case, the team keeps the challenge because no ABS check took place.
Dault pointed out the odd sight of a player acting before his manager can weigh in. Steve Ford had an example from a clip he remembered seeing: Jazz Chisholm challenged a called third strike that Ford thought was clearly in the zone. Ford laughed at the decision. Dault imagined the manager wondering why a player had spent a team challenge on it.
Managers can still set expectations. MLB reported that some clubs planned to have pitchers leave the choice to catchers. Once a pitch is called, though, the person tapping the helmet owns the moment.
How many ABS challenges does each team get?
Each team starts with two. The number is easier to understand as two chances to be wrong: an overturned call does not use one up. A confirmed umpire call does.
Say a catcher challenges a ball and ABS shows a strike. The call changes, and the team still has two challenges. Later, a hitter on that same team challenges a strike that ABS confirms. Now the team has one.
Dault compared the habit of saving challenges to other sports’ replay systems. The key difference here is who makes the request. A baseball manager may wish the team would save its last challenge, yet the batter at the plate can tap anyway.
Extra innings give teams a little protection. If a club begins the 10th with no challenges left, it gets one for that inning. If it uses and loses that one, it gets another at the start of the 11th. A team that still has a challenge when an extra inning begins does not get another for that inning.
“Sometimes umps call strike zones very different, right?”
The remaining number appears on the ballpark scoreboard. It is worth checking before a close pitch in the ninth. A team with one challenge left faces a different choice from a team that has kept both.
What counts as a strike on an ABS review?
The ABS zone is 17 inches wide, the same width as home plate. Its top sits at 53.5% of the batter’s measured height, and its bottom at 27%. Players are measured standing straight without cleats.
The system checks the ball as it passes through the middle of the plate. That detail matters. A pitch that nicks the front edge and then drops may look very different from a pitch crossing the zone’s middle. MLB tested other versions before choosing this one.
It can still be surprising to watch. A pitch may miss by a sliver, even when it looked good from the couch. On a broadcast, the usual strike-zone box is a handy guide. The ABS result decides the challenge.
An overturned call can do more than change the count. A called third strike can become ball four, turning a strikeout into a walk. A called ball four can become strike three. That is a large change for a pitch that took less than a second to reach the catcher.
Other action may stand. MLB gives the example of a runner stealing third on a full-count pitch called a ball. If ABS changes that pitch to strike three, the batter is out, but a runner who stole third safely can stay there. Umpires judge whether the original call affected what happened on the bases.
Why does an ABS challenge change game strategy?
A challenge belongs to the team, even when one player makes it. That creates a small argument inside every close call. The hitter wants another chance right now. His teammates may want a challenge left for later.
A called strike one with nobody on in the second inning is worth fixing. But losing a challenge could hurt in the ninth. A called strike three with two outs and the bases loaded is much harder to leave alone.
Baseball Savant’s study of Triple-A games in 2025 found that hitters challenged more often with two strikes. They challenged about 20% of eligible calls in those counts, compared with just under 5% overall. The urge makes sense. Strike three ends the trip to the plate.
Desperation did not make hitters better judges. Their challenges succeeded 45% of the time overall in that Triple-A study, but only 36% of the time with two strikes. Those minor-league figures are useful context, though they should not be treated as a prediction for every major-league hitter.
There is a catcher’s choice, too. He may think a called ball caught the edge, yet know that one wrong tap leaves his team with nothing for a later inning. Good judgment means knowing when a close pitch is close enough to leave alone.
Ford’s Chisholm story gets at the human side of this. A player has about two seconds to decide. The rest of the club gets plenty of time to discuss it afterward.
Does ABS slow games down or replace umpires?
Dault was torn on both points. He liked getting the call right, and thought the replay result came quickly. Still, he remembered watching a Brewers game and growing tired of repeated challenges as the game wore on.
The testing gives that complaint some scale. In 288 spring training games in 2025, MLB recorded an average of 4.1 challenges per game. Each took about 13.8 seconds on average, adding roughly 57 seconds per game. That is a short delay on paper. In a tense inning, it can feel longer.
Nor does ABS mean that umpires have stopped calling balls and strikes. They make the first call on every pitch. Players have limited chances to contest it, and most pitches never get a head tap. Catchers still work behind the plate with a human umpire watching the ball.
Dault saw a possible path toward a future with less human judgment. He did not claim MLB had already taken that step. His point was more personal: he likes the game’s human element, even as he wants a big call to be right.
That tension fits the system rather well. The umpire calls strike. The batter taps his helmet. For a few seconds, the whole park waits to see who saw it better.
The full episode of Long Gone is on Underdog Podcasts, with the rest of the network's shows.
People also ask
Can an MLB manager challenge a ball or strike call?+
No. An ABS challenge must come from the batter, pitcher, or catcher. The player signals by tapping a cap or helmet promptly after the call, without help from the dugout. Managers can discuss how they want their players to use challenges, but they cannot make the request during an at-bat.
Do MLB teams lose a challenge if they win it?+
No. Each team starts with two challenges and keeps one whenever ABS overturns the umpire’s call. The team loses a challenge only when the review confirms the original call. That means a team can make more than two successful challenges in a game, provided it still has one available to request each review.
Do teams get more ABS challenges in extra innings?+
A team that begins an extra inning with no challenges left receives one for that inning. If it loses that challenge and the game continues, it receives one at the start of the next inning. A team that already has a challenge when an extra inning starts does not receive an additional one for that inning.
Can players challenge every pitch in MLB?+
No. ABS reviews a called ball or strike only when an eligible player makes a timely challenge and the team has one available. Players cannot use it to review a swing. MLB also does not allow ABS challenges when a position player is pitching or after a replay review.