As we enter the final week of the 2025 MLB regular season, the league has made a significant announcement, stating that it will implement an Automated Ball-Strike Challenge System for the entirety of the 2026 season.
What is an ABS challenge system?
The ABS challenge system is not "robot umps," as many had feared would come to baseball. Instead of being an automated system that calls every ball and strike, the ABS Challenge System allows teams to request a review of important ball-strike calls during a game. It's a balance between a fully technological system and the current system that includes natural human error from the very human umpires.
If you've watched a tennis match, then you already know how this ABS system will work. After a given pitch is delivered during a game, a batter, catcher, or pitcher will have a narrow window of time to challenge the call the umpire made. Once a challenge has been made, the umpire will inform the stadium that the pitch is being challenged, and everyone, including the players and umpires, will watch the Jumbotron that every stadium has in the outfield. The screen will show an animation that depicts the path of the pitch, and then, when the pitch crosses the plate, it will pause and highlight the location of the pitch as it crossed the plate to see if any part of the ball knicked the strike zone in the slightest bit. If the animation shows that the pitch was a strike, the pitch must be called a strike, regardless of what the umpire had called before, and vice versa.
How will the ABS system work in baseball?
MLB stadiums are equipped with Hawk-Eye technology that already monitors the exact spin, movement, and location of each pitch, relative to the batter’s zone. That's how we get all of our advanced pitch mix data over the last few seasons. Players will now be able to use that technology to request a challenge of a ball or strike call if they think the umpire got it wrong.
Unlike in the NFL, where a coach has to throw a challenge flag, in MLB games, managers will not be able to challenge. Challenges are only allowed to be initiated by a pitcher, catcher, or batter, and they will do so by tapping their hat or helmet to let the umpire know.
This system is designed to prevent any help from the dugout or other players on the field, which will limit any player from getting outside feedback from a team's own technology to tell him that he should challenge. The challenge must also come immediately after the ball or strike has been called, so players will get no time to deliberate and wait for a teammate or coach to yell something to them.
This ABS system will work by creating a unique strike zone for each batter. This was something that Guardians catcher Austin Hedges was worried about when I spoke to him during spring training. Austin Hedges told me that his biggest fear with an ABS system was that the league needs "to figure out what that strike zone means. I worry about having a different strike zone for every hitter, and now the umpire has to know what that strike zone is for each measured zone."
As outlined by The Athletic, the zone will also be created using technology: "The ABS zone for each player is based on measurements taken by one independent party and verified by another; the top of the zone is defined as 53.5 percent of a player’s height, and the bottom of the zone is 27 percent of their height. The zone is 17 inches wide — the width of home plate — and pitch location is measured at the midpoint between the front and back of the plate. Any part of the ball only needs to tick the edge of the zone to be a strike."
Of course, the issue here is that umpires will need to be able to quickly adjust the strike zone to that specificity for every single hitter during a game or risk getting calls wrong.
Another wrinkle in how this will work is seeing how teams devise a strategy for deciding who can issue a challenge. Data has shown that catchers tend to be the most accurate in terms of determining balls and strikes, which seems obvious, but managers may prevent some issues with a poor understanding of the strike zone by issuing a challenge. Managers may also prevent their team from challenging pitches early in the count or early in the game because they don't want to risk being out of challenges in the crucial final innings. It will be an interesting and exciting new level of strategy for MLB managers.
How many ABS challenges per game in MLB?
Each team will get two challenges at the start of the game, and they will be able to keep the challenges if they're successful, so we could rephrase that to say that each team gets two incorrect challenges a game. Even if that seems like a recipe for infinite challenges, previous data has shown that to not be the case. According to Baseball America,"On average, there were 4.2 ABS challenges out of the roughly 290 pitches thrown per Triple-A game in 2025."
In each extra inning, a team will be given an additional challenge if it has none remaining entering the 10th inning. If they use the challenge, they will get a new one at the start of the 11th inning. If a team does have challenges remaining entering extra innings, they will not be given a new challenge, but they will be granted an additional one if they use their remaining challenge in the 10th inning.
Which baseball leagues are using automated systems?
MLB has been experimenting with many different forms of ABS systems in games since 2019. Back in 2019, the Atlantic League, which is an independent league run in conjunction with MLB, adopted a full ABS system, which is more casually referred to as "robot umps," where technology called every pitch in the umpire's ear. The Challenge System was then used for the first time in 2022 in the Florida State League. For the two seasons after that, 2023 and 2024, Triple-A teams tested both the Challenge System and the full ABS system. By the end of the 2024 season, it had become clear during feedback that the challenge system was more popular with players and fans, which is why it was tested in MLB spring training this season.
Will the ABS system impact the length of the game?
As Baseball America reported in the same article linked above, "the ABS challenge system hasn’t really affected game time in Triple-A." Much like in tennis, these challenges are quick, so this will not be similar to lengthy NFL and NBA replays that can often sap the momentum of the game. According to an MLB release, "In 288 games with the ABS Challenge System during Spring Training 2025, there were an average of 4.1 challenges per game, and those challenges took an average of 13.8 seconds." That means the Challenge System would add approximately one minute to each game.
How accurate is the ABS system in baseball?
According to the same MLB press release, during the 288-game experiment during spring training, calls were overturned 52.2% of the time. As we noted above, catchers had the best success rate at 56%, while hitters were successful 50% of the time, and pitchers were successful just 41% of the time.
It is important to note that there is a margin for error with the Hawkeye technology, as there is for all technology. As previously reported by The Athletic, the league has "acknowledged the margin for error’s presence," but had not, at that time, told players exactly how large the margin was.
How will ABS impact catchers?
One of the immediate reactions to the challenge system is that it will impact the value of catchers being strong framers. Hedges mentioned that he had some concerns about what the ABS system would do for defensive catchers like himself: "I don't know if it's gonna be enough to make [framing] not as important, but it's definitely gonna take a little bit away from receiving."
While it may impact receiving in a small way, because the catcher can fool an umpire with good framing and then have that call challenged, it's unlikely to have a major impact on framing. As Giants catcher Patrick Bailey said in an article with The Athletic, "I don’t think it’s going to take away the value of framing. You still have to get calls and keep strikes (as) strikes. At the end of the day, I still think it’s going to be really valuable to know the zone.”
Bailey's point is a crucial one here. For a strike to even be challenged, the catcher has to get the strike first. He still has to present it successfully to the umpire. If he does get that strike call, it's not a given that the opposing team will challenge since they only get two missed challenges a game. Are you willing to risk that in the second inning on an 0-0 pitch? That may not seem like a significant pitch in the overall course of the game, but it's huge for a pitcher to be in a 0-1 count versus a 1-0 count. That could drastically reshape an entire inning, so the value of framing absolutely will still exist.
In the ABS challenge system, the vast majority of pitches are still going to be called by the umpires, so catchers being able to get those borderline called strikes called will still have tremendous value. A really good framing catcher could also make it hard on opposing teams to know when they should challenge or not, which adds an extra layer of strategy, while a poor framer may force himself or his pitcher to use more challenges to get ball calls reversed because the catcher framed a strike poorly.
For every player, it will make an understanding of the strike zone even more important.
“I don’t think it’s going to change the game as much as I originally thought it would,” Bailey said. “I think it’s just going to take away the really big misses.”
That's something everybody can get behind.
