The Automated Strike Zone Is Slightly Different At Triple-A in 2023

Image credit: Triple-A Umpire Matt Bates Using The ABS System (Photo by Erica Denhoff/Icon Sportswire via Getty Images)

The automated ball-strike system is getting an expanded run at Triple-A this year with a few key adjustments.

The automated ball-strike system (ABS), known colloquially as robo-umps, uses the Hawk-Eye tracking system to determine whether a pitch is a ball or strike and relays the call to the home plate umpire via an earpiece. ABS was used in 11 Triple-A stadiums last year and was expanded to all 30 stadiums this year. The Pacific Coast League has been using ABS since Opening Day. The International League began using it April 25.

There are two key differences in how ABS is being used this year at Triple-A.

The first is that “full” ABS, where the system determines balls and strikes, is only being used for the first three games of each series. The final three games of each series are using a “challenge” system where the home plate umpire calls balls and strikes and teams can challenge calls. ABS is used to verify whether the call was correct or not.

“The purpose of doing both is to see them side by side in the Triple-A environment and hope that one emerges as the clear favorite of fans, players (and) coaches,” Sword said. “And then I guess a sub question would be if there are any modifications to that preferred format.”

The challenge system was only used the final month of last season in select parks at Triple-A—Charlotte, Round Rock, Sugar Land, Tacoma and Las Vegas—and only on select days. Even in that limited time, it quickly became the preferred option among players and coaches, leading MLB to expand its use in 2023. The challenge system was also used in select Arizona Fall League games after last season.

Each team gets three challenges and retains a correct challenge. Challenges can only be initiated by the pitcher, hitter or catcher and must be made immediately after an umpire’s call.

“Challenge was more popular in our polling of players and coaches that played with both systems,” Sword said. “We’ll do that polling again this season to see whether that result holds.

“Among fans, it’s a tricker question because the whole idea of ABS is a fan wouldn’t even notice it was being used because it’s just a very subtle earpiece in the umpire’s ear. Whereas the challenge system actually has an entertainment component, which is the result of the challenge goes up on the video board and people get to see in real time where the pitch was.”

Aside from player popularity, the other benefit to the challenge system is it preserves the importance of catcher framing as a skill. With full ABS, there is no need for catchers to frame pitches in a way that preserves or steals a strike. With the challenge system and umpires still calling balls and strikes, that skill retains value.

“One issue people have raised with us is the catching position,” Sword said. “The importance of catcher framing is impacted significantly by a full ABS system where the way that you receive pitches just doesn’t matter anymore.

“In the challenge world, that effect is mitigated significantly where that skill is still valuable. There are a whole host of other issue related to that format choice that we’re thinking through, but again, that’s the purpose of this season.”

There are two main reasons MLB chose to run full ABS and the challenge system side-by-side during the same series as opposed to playing the first half with one system and the second half with the other. The first reasons involves umpires and the second is due to the roster churn that naturally occurs over the course of a season.



“We’re trying to balance a lot of priorities here,” Sword said. “One is the umpires in Triple-A, many of them appear in the major leagues throughout the season, and we wanted to make sure those guys had an opportunity to call plate games regularly throughout the season so that when they came up to the big leagues they had done it recently and felt fresh. That was a big reason.

“The other thing is we thought it would be easier for the players and coaches to give us a comparison of the two formats as they sort of see them side-by-side all the time rather than one half and the other. Sometimes there’s pretty significant turnover in the roster half to half and it’s a little tricker to get great feedback on the type of format. So we thought that approach made sense.”

The other major change is the strike zone used by ABS at Triple-A has been narrowed from 19 to 17 inches—the exact width of the plate. MLB made the change after seeing an elevated number of strikeouts in ABS-called games compared to non ABS-called games last season.

It is the latest change MLB has made in an ongoing quest to find the “optimal” strike zone to use with ABS.

ABS was first introduced in the affiliated minors in the Low-A Southeast (now Florida State League) in 2021. After walks skyrocketed and the length of games increased, MLB adjusted the size and shape of the strike zone midway through the season. The league eliminated three and a half inches off the top of the strike zone, widened it by two inches on each side of the plate and changed where pitches were registered from the front to the middle of the plate.

The introduction of the challenge system in 2022 was another way to address concerns about the strike zone being called by ABS. This year the zone is different again.

The strike zone this year at Triple-A is a two-dimensional strike zone that is 17 inches wide. Pitches are registered in the middle of the plate.

“The second question (we’re trying to answer), which is also a very tricky question, is the geometry of the zone,” Sword said. “And coming up with a strike zone to load into that system that will produce ball-strike calls that make sense to both teams and promote the kind of on-field outcomes that we are seeking to promote. That is, we are finding, a very tricky problem. We’re hoping to make some progress on that question this year.”

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