Everything You Need to Know About MLB's ABS Challenge System

Major League Baseball will be instituting the ABS (Automatic Ball and Strike) challenge system for 2026. Previously used in Spring Training 2025 and throughout the minor leagues over the last several years, the league has determined the system is ready for primetime.

What follows is a detailed breakdown of how the system operates and how it will be implemented, based on a presentation from MLB during media day in Arizona at the start of Spring Training. You can also read comments from Torey Lovullo and Mike Hazen to learn how the Arizona Diamondbacks are approaching this new system.

MLB ABS Challenge System Primer

What is the Goal and Objective of the Challenge System?

"Provide players with an opportunity to correct missed calls in high-leverage moments in a manner that fans like."

Few things in the game create discord amongst fans, players and umpires more than missed calls during key moments. The goal of this system is to give players and teams an opportunity to get missed calls corrected.

ABS Challenge Regulations

Each teams starts the game with 2 challenges

Correct challenges are retained

Challenges may only be made by the pitcher, catcher, or hitter.

Runners placed based on umpires’ determination if incorrect call impacted player behavior.

A pitch may not be challenged if a position player is pitching.

Additional challenge at the start of each extra inning that a team would otherwise have no challenges.

An example of the extra inning rule: if at the conclusion of the ninth inning the visiting team had two challenges remaining, and the home team had none, the visiting team would still retain two challenges in the tenth inning, while the home team would receive one new challenge.

ABS Strike Zone

The width of the zone is 17 inches, which is the width of home plate.

The top of the zone is 53% of the height of the player, and the bottom of the zone is 27% of the height of the player.

The strike zone depth is at the midway point between the front and back of the plate, i.e. 8.5 inches.

Each MLB player is measured in a uniform manner at the start of Spring Training.

Requirements for a Challenge to be Accepted

Batter, pitcher or catcher must tap their hat / helmet to challenge. Players are encouraged to simultaneously verbalize the request to challenge.

Challenges must be initiated immediately after the prior pitch (~2 seconds). If there is an ensuing play (e.g., checked-swing appeal, play on a runner), the challenge may be made and accepted at the conclusion of the ensuing play.

Player’s decision to challenge must be unaided. No help from other defenders, runners, or the dugout. If the umpire determines player’s decision was aided, challenge request shall be denied (team will retain its challenge).

Disallowing a Challenge

Points of Emphasis

Timeliness of the challenge
Player or runner on the field tapping their hat / helmet
Player obviously looking into the dugout before challenging

Other Safeguards

MLB has instituted a delay on all pitch location data (e.g., Gameday App)
Broadcast feed with strike zone box will not be available live (minimum delay of 9 seconds)
Prohibition on club-owned ball-tracking systems (e.g., TrackMan)
MLB will review video from all challenges and monitor for suspicious behavior

Scoreboard Requirements

A video graphic will appear on stadium scoreboards within seconds of the challenge, allowing fans to see exactly where the pitch landed. If any part of the ball touches the edge of the zone, it's a strike.

Balls and Strikes

In-park scoreboard and ABS Graphic will use the same data source.

Challenges Remaining

Clubs are required to display the number of ABS Challenge remaining on the main scoreboard in the scoreline, signified by the code “ABS."

ABS Challenges remaining will replaces mound visits remaining in the scoreline – MVR is still required to be prominently displayed in a place that is easy for the umpire and dugouts to view.

Runner Placement Rules

General Rule:

If the umpires determine that an incorrect call of ball or strike had no effect on subsequent behavior, the umpires will let stand any calls unaffected by the incorrect ball/strike call.

Any doubt regarding the placement of runners should be resolved in favor of the last base legally touched at the time of the challenge.

Relevant if: (1) call is overturned, and (2) original call or the result of the challenge would end the plate appearance.

Special Circumstances:

Overturn from ball to strike and pitch dropped by catcher – batter is out without requiring the batter or first base to be tagged.

Interplay with Video Replay

ABS & Replay Challenges on the same pitch:

No ABS Challenges following Replay Reviews (avoids complex series of challenges).

If there is potential for a review following an ABS Challenge, umpires will check that neither manager wants to initiate a replay review before restarting the clock.

If a manager want to challenge a play following an ABS Challenge, the request must come immediately after the conclusion of the ABS Challenge (i.e., no 15-second manager hold).

If requested simultaneously, the umpire will accept the ABS Challenge first then prompt managers for replay challenge.

Play types that are most likely to be impacted are plays on the bases (e.g., stolen base attempts, pickoffs) and HBP.

2026 Spring Training & WBC

ABS will be used for all Spring Training games played between two MLB clubs at MLB Spring Training or MLB ballparks.

No ABS when MLB Club scrimmages a college or WBC team.

No ABS for games played in non-MLB Spring Training venues (e.g., Dominican Republic).

Tempe Diablo does not have a video board – the result of all challenges will be relayed verbally by the ABS Operator.

ABS will not be used in the World Baseball Classic.

OTHER POINTS OF NOTE

Based on past experience MLB expects strikeout rate to decrease slightly and walk rate to increase slightly.

The average number of challenges per game in both Triple-A and 2025 spring training has been roughly four, and the number of overturned calls hovers around 50%.

The percent of challenges used in the regular season will skew towards the later innings. In spring training they will skew towards the earlier innings when major league roster players are more likely to be in the game.

The total added time to the average time of game to handle reviews is approximately one minute. In 2025 the average time of game was 26 minutes less than in 2022 prior to the institution of the pitch clock. This means that ABS challenges will have minimal impact on the time of games.