An ABS challenge system lets a small group of players on the field push back on a home plate umpire’s ball or strike call, sending it to an automated tracking system for an instant, precise review. Major League Baseball adopted it league-wide for the entire 2026 season, and the sport has not looked the same since. Here’s exactly how it works, why MLB built it this way instead of automating every call, and what the same technology now means for baseball and softball below the professional level.
How the ABS Challenge System Actually Works
ABS stands for Automated Ball-Strike. The “challenge” part of the name is the key detail: a human umpire still calls every pitch behind the plate, the same as always. Players just get a limited number of chances per game to ask a camera-based tracking system to check a specific call.
The mechanics are simple and fast:
- Who can challenge: Only the pitcher, the catcher, or the batter involved in that pitch. Managers, coaches, and teammates in the dugout cannot initiate or help with a challenge, and umpires can deny a challenge if they believe outside help was involved.
- How to challenge: The player taps their cap or helmet within roughly two seconds of the umpire’s call. No verbal argument, no delay, no signal from the bench.
- Challenges per team: Each team starts the game with two challenges. A successful challenge is retained, so a team that keeps winning its challenges never runs out. A team that loses two challenges is done challenging for the rest of the regulation innings.
- Extra innings: A team that enters extra innings with zero challenges remaining is awarded one for that inning, whether or not they had exhausted their challenges in the first nine.
- Review time: The tracking system checks the pitch location against that batter’s own strike zone and returns a result in about 15 seconds, shown on the stadium video board and broadcast.
- The technology: MLB’s system runs on 12 Hawk-Eye optical tracking cameras per ballpark connected over a private 5G network, measuring where the pitch crossed the plate against a strike zone sized to the individual hitter (roughly the top 53.5% to bottom 27% of that player’s height), not a fixed box.
Since Opening Day of the 2026 season, MLB teams have used the system heavily. By the trade deadline, more than 7,100 challenges had been issued league-wide, with a 53% success rate for the team doing the challenging, and teams averaging just over four challenges per game.
Why a Challenge System and Not Full Automation?
MLB had another option on the table: a full-ABS system where the camera calls every single pitch and the human umpire’s job is just to relay it. The league chose the challenge model instead, and the reasoning matters for understanding where the technology is headed.
A challenge system keeps a human umpire calling the game in real time, which preserves game flow and the sport’s long relationship with in-game officiating, while still correcting the handful of calls per game that actually matter most. Full-ABS removes that judgment entirely. Both models have already been tested extensively below the MLB level:
- The independent Atlantic League first used a full-ABS system, nicknamed “robot umps,” during its 2019 all-star game, with umpires receiving ball-strike calls through an earpiece.
- The Arizona Fall League ran full-ABS starting in 2021, and it drew real criticism for calling breaking balls strikes even when they dropped out of the zone by the time they crossed the plate.
- Triple-A and MLB spring training tested both the full-ABS and challenge models for several seasons before MLB settled on the challenge system for 2026.
That testing history is exactly why MLB landed on the challenge model: it fixes the calls players actually dispute without removing the umpire from the game entirely.
Who Else Is Using ABS Challenges
MLB’s adoption is the headline, but the challenge system is spreading fast. The NCAA rules subcommittee has approved ABS challenges for college baseball beginning in 2027, and the SEC ran a live test of the system during its 2026 conference tournament to get ahead of that timeline. Programs that wait until the NCAA’s official 2027 start will be a full year behind teams that have already run the system in real games.
Bringing ABS Challenges to Youth, Travel, and Amateur Baseball
MLB-level ABS technology is not just a professional-level tool anymore, and the gap it closes at the amateur level is different from the one it closes in the big leagues. In the majors, the challenge system exists to fix the handful of calls that go wrong even with a well-trained, full-time crew. At the travel and youth level, the more basic problem is that there often is not enough crew to begin with.
The National Association of Sports Officials has tracked the average age of baseball officials rising to roughly 54, based on its own membership survey, and travel tournament directors report the same recruiting problem from the ground: fewer new, younger umpires entering the profession to replace the ones aging out. A tournament running 12 games across 3 fields on a Saturday can genuinely run short of qualified crews, which is exactly the kind of gap this technology was designed to close in the first place. Even professional-level umpiring, which benefits from full-time training, runs at roughly 94% ball-strike accuracy according to independent tracking site UmpScorecards, meaning even the best human crews miss a real number of calls across a typical 150-pitch game. A consistent, camera-based zone removes that variable at the level of baseball where it can least afford a shorthanded or inexperienced crew.
WIN Reality’s SmartPark brings this same category of technology to travel, high school, and college fields. A fixed optical camera system tracks every pitch and displays an Automatic Balls & Strikes call on an LED board next to the field, running either as a full-call system or a challenge model depending on how a program wants to run it. The underlying camera and tracking setup is the same one that powers SmartPark’s broader data capture: 125+ live metrics drawn from the optical system’s core game and ball tracking, with additional bat sensor and swing biomechanics data layered in through integration with Blast Motion and SwingAI. SmartPark supports both baseball and softball fields, and every WIN Reality SmartPark already runs an ABS Challenge operation built to the standards accepted for NCAA competition, ahead of the league’s own 2027 rollout.
For a program dealing with an actual umpire shortage rather than just an occasional missed call, that consistency is the difference between finishing a tournament on schedule and cancelling games because a crew never showed up.
Frequently Asked Questions
What does ABS stand for? Automated Ball-Strike. The “challenge system” specifically refers to the version where a human umpire calls the game and players can request an automated review of specific pitches, as opposed to a full-ABS system that calls every pitch automatically.
How many challenges does each team get? Two per game in MLB’s system, and a team keeps a challenge every time it wins one. A team loses its remaining challenges for the rest of regulation innings after two failed challenges. Teams get one additional challenge per extra inning if they have none remaining.
Who is allowed to challenge a call? Only the batter, the pitcher, or the catcher on the field for that pitch. No one else, including coaches and the dugout, can initiate or assist with a challenge.
Does this technology exist below the MLB level? Yes. The NCAA has approved ABS challenges for college baseball starting in 2027, with the SEC already testing it in 2026, and systems like WIN Reality’s SmartPark bring the same category of optical tracking and automated calls to travel, high school, and college fields today.
The Bottom Line
An ABS challenge system is not a robot umpire replacing the crew behind the plate. It is a fast, precise check on the handful of calls a game actually turns on, run by players instead of managers, and it is moving from MLB into college baseball and now amateur fields faster than most programs realize.
