When and how will robot umps arrive in the majors? Latest on MLB’s plan

Major League Baseball sent a memo to all 30 teams Tuesday that shed some light on how the sport views the future of the automated balls and strikes system — or ABS — in the majors.

Beginning June 25, all Triple-A games will move to a challenge system; since the start of the 2023 season, a fully automated strike zone was also being tested at the level.

The announcement shows that the league is leaning toward implementing a challenge system in the majors, but important details — when it could arrive, specifics of the system and what technology will be used — still need to be decided. Here is what we know and don’t know about the future of ABS in MLB.

Why is MLB moving toward a challenge system instead of a fully automated strike zone?

MLB has been testing both options in Triple-A since last season, with a challenge system for weekend games and automated balls and strikes during the week. The league’s research showed a strong preference for a system built around a set number of challenges per game, rather than an automated strike zone or the current MLB process of umpires making calls without technology.

“The support for challenge over complete ABS is overwhelming, from players and fans,” commissioner Rob Manfred told ESPN.

According to MLB, 61% of team personnel (including players) and 47% of fans favor a challenge system, compared to 28% of team personnel and 30% of fans preferring to stick with the current no-technology system and just 11% and 23% wanting full ABS.

How will the challenge system work in Triple-A for the rest of this season?

Now that MLB is moving toward a challenge system, it must decide the number of challenges each team will receive per game, and the league will use Triple-A games to help decide that. In Pacific Coast League games, each team will get three challenges, while in the International League each team will have two.

After polling fans, league officials believe fewer challenges are preferred and want to see how that plays out on the field. Since teams retain their number of challenges if they win, the actual number used in a game has reached double digits and “weighed down” the pace a bit, according to league sources. MLB wants to see if limiting the number of challenges will force teams to be more conservative in using them.

The commissioner has said ABS won’t be ready for the majors next season — why not? And when could it be ready?

The earliest would be 2026. Perfecting the technology is part of it, but just as important to the league is avoiding implementation at the highest level until MLB is sure that it’s the right step to take for the game.

Once the changes reach the majors, Manfred feels this is a move the league can’t go back on, so he wants to be certain. There’s precedent for this kind of timeline, too: The pitch clock and shift ban also were tested in the minors for multiple seasons before arriving in the major leagues.

What are the biggest technological questions that must be answered first?

Setting the top and bottom of the strike zone for each player presents the biggest technological hurdle MLB has yet to clear.

“There are two things you have to do,” Manfred told ESPN. “One is measure the track of the ball. We’re good there. The second thing you have to do is set the strike zone for each batter and we’re not there yet.”

Essentially, the league has two options: A height-based zone or a stance-based one.

A height-based zone is the simplest option: Players would be measured before each season and their strike zone would be set accordingly. Everyone at the same height would have the same zone, without taking into account the difference in stances for each player.

A stance-based zone revolves around camera readings of a player’s knees and hips as the pitch travels to home plate. The top and bottom would then be set based on a rolling median of the last 50 pitches seen by the batter — so hitters would not be able to get around the system by changing their stance depending on the count or situation in the game.

It’s a hard system to get right. This kind of zone would actually differ more from the current, human-umpire zone than the height-based approach would, forcing players to adjust in a more dramatic way.

There are other kinks to work out. For example, as cameras attempted to capture the belt on a player to help set the zone, they had some troubles finding it on those players whose jerseys hung over their stomachs. Those things must be remedied before the technology is ready for the big leagues.

How could ABS change the game on the field? Could it actually help offense in MLB?

Moving to a fully automated system could have given MLB teams a chance to set the strike zone of their choosing and, in theory, shrink it in hopes of it leading to more offense. But the league’s research shows that high strikeout totals in MLB aren’t necessarily coming at the edges of the zone as much as they are in the zone — likely due to higher velocities, not the zone — so the impact of a smaller zone might not ramp up offense that much.

For younger players, at least, implementing the automated zone would lessen the learning curve in the majors: Many of those called up in recent seasons have expressed issues with adjusting to the human umpire strike zone after having an automated zone in Triple-A. Essentially, the full ABS zone is a rectangle, while the human zone is more of an oval. In the challenge system, the calls being reviewed are often egregious misses rather than pitches just off the plate so slight differences in the strike zone become less important.