RoboUmp Hits the Big Leagues: A Comprehensive Digest

Major League Baseball is introducing robot umpires—but not in the way anyone expected. This episode of 99% Invisible, originally broadcast in 2023 and updated with new material, explores the tension between accuracy and humanity in America's pastime, tracing the journey from a disastrous 1997 playoff game marred by egregious umpiring to the 2025 rollout of the ABS (Automatic Balls and Strikes) challenge system. Host Roman Mars and producer Chris Berube deliver a nuanced, often surprising look at what happens when you replace human judgment with machine precision, and why the result might be more drama, not less.

0:00The Problem with Human Umpires

The episode opens with a vivid example of why robot umpires are even being considered: the 1997 National League Championship Series, where Florida Marlins rookie pitcher Livan Hernandez struck out 15 Atlanta Braves batters. Baseball analyst Katie Nolan recalls watching in disbelief as umpire Eric Gregg called strikes on pitches that were "a foot, two feet outside of the strike zone." The outside corner of the strike zone "just didn't end," she says—it was "a never-ending strike zone." Hernandez's team won that game and eventually the World Series, leaving Braves fans to wonder what might have been.

This is not an isolated incident. A 2018 study found that Major League Baseball umpires blow about 14 calls per game, totaling 34,000 bad calls every season. While umpires get balls and strikes right about 94 to 97 percent of the time—an impressive figure given that pitches travel at 95 miles per hour—those errors can decide championships. The home plate umpire, who calls every pitch a ball or a strike, has the most consequential job in the sport. And as producer Chris Berube notes from his own experience as a teenage umpire, "getting calls right is a lot harder than it looks."

6:47The History of Robot Umpires and the ABS System

The idea of replacing human umpires with machines is not new. In the 1950s, the Brooklyn Dodgers tested a robot umpire designed by General Electric—a large machine that "kind of looked like a barbecue hooked up to a specially tricked out home plate." If the ball cast a shadow over the plate, the machine would light up a red button indicating a strike. The problem: it didn't work well, and at night games, it didn't work at all. The technology simply wasn't ready.

Today's "robot umpires" are not actually robots. As New Yorker editor and sports writer Zach Helfand explains, the modern system is "a series of HD cameras" called the Integrated Camera Baseball Tracking system. Most major league stadiums already have these sophisticated tracking systems installed for TV broadcasts, using missile-tracking technology to measure every pitch's location, spin rate, and velocity. The data is displayed to viewers as charts and scatter plots showing where the ball crossed the plate—but until now, umpires themselves did not have access to this information.

Since 2019, the system—officially called ABS for Automatic Balls and Strikes—has been tested in the minor leagues. In Triple A, the highest minor league level, the ABS system worked in collaboration with human umpires: the robot made the call, and the human umpire announced it through an earpiece. Fred DeJesus, the first umpire to use the system in 2019 (whose earpiece is now in the Baseball Hall of Fame), says he was initially wary but came around quickly. "When in Rome, you do what the Romans want," he says. "They wanted you to follow the system, you call it." DeJesus reports the system was "very accurate," with only minor glitches.

14:20The Trade-Off: Accuracy vs. Charm

But accuracy is not everything. Helfand argues that "most people don't watch sports to see the fairest or most accurate outcome." The real tension, he says, is "efficiency and accuracy versus charm and drama and dialogue." Baseball has been played and umpired by humans for over a century, and in that process, the sport has accumulated "lots of small quirks and inefficiencies." Stadiums have non-standard dimensions; a home run at Fenway Park might be a routine fly ball at Dodger Stadium. Similarly, the strike zone itself is not applied uniformly.

The textbook strike zone runs from a player's chest to their knees over the plate. But human umpires routinely call strikes on pitches that are "hittable" even if they fall outside the textbook zone. When the ABS system was first introduced to the Atlantic League in 2019, it was programmed to call the textbook strike zone—and fans and players hated it. The robot was calling too many hittable pitches as balls, dragging games out. The league had to reprogram the ABS to be *less* accurate, expanding the strike zone by about an inch to an inch and a half off the plate to better match what humans actually call.

More fundamentally, human umpires adjust the strike zone based on context. As Helfand explains, "When a pitcher is struggling, there's a demonstrable effect that the umpire zone gets bigger. Sometimes it gets as much as 50% bigger." This is called "the compassionate umpire effect"—a subconscious effort to help a struggling pitcher. When it's raining, umpires expand the zone to move the game along. When one team is ahead by a lot, they do the same. These are "small imperfections that makes baseball kind of romantic," Helfand says. "You do lose these quirks, these injustices, these twists of fate where someone blinks or gets dirt in their eye and they make a bad call and that changes everything."

17:30The Human Cost of Umpiring

The episode also examines the darker side of human umpiring: the abuse. Katie Nolan describes the job's reality: "Imagine going to work knowing you could get a shard of wood directly into your face, or you could get hit by a 100 mile per hour projectile in the face. On a bad day and on a good day, the ceiling of this job is like, you make calls that get people to tell you that you suck at your job and you're the worst and you ruined the game."

Berube shares his own experience: after making a bad third-strike call in a little league game, a coach waited for him in the parking lot to yell at him. "The abuse is actually the primary reason that I stopped umpiring," he says. There are stories of umpires receiving death threats and being physically assaulted. In one incident described in the episode, a Staten Island parent coach punched an umpire so hard it left him with a broken jaw.

This is where the robot umpire offers an unexpected benefit: it lowers the temperature. Helfan observed this firsthand at a minor league game. Fans who were heckling the umpire suddenly stopped when they realized the calls were coming from the machine. One fan pointed up at the hardware above home plate and said, "It's not the umpire. This is just the strike zone." The fan was "humiliated in a certain way, very humbled," Helfand says. Berube noticed a similar moment during the Isotopes-Chihuahuas game: a batter disagreed with a call, started to turn toward the umpire to yell, then stopped himself and walked back to the dugout. "I'd never seen that before," Berube says.

25:57The 2025 Update: The Challenge System Arrives

The original episode was broadcast in 2023. In the update, Berube reports that robot umpires have arrived in Major League Baseball—but not in the way anyone predicted. Instead of the full robot system where the machine makes every call and the human announces it, MLB has implemented a "challenge system." Human umpires still make every ball and strike call, but players can challenge calls they disagree with. The ABS system then determines who was correct.

Here's how it works: after a pitch, either the catcher, hitter, or pitcher taps their helmet to signal a challenge. The umpire acknowledges, and within about 10 seconds, a graphic appears on the scoreboard showing the ball's trajectory and whether it crossed the strike zone. The ABS then announces whether the call stands or is overturned.

To prevent the game from slowing down, each team gets only two challenges per game—but successful challenges are retained. "So basically, each team gets the right to be wrong twice," Berube explains. This incentivizes players to challenge only on important or borderline plays where they are confident they are right.

28:57Early Reactions: Drama, Humiliation, and a Viral Moment

Early reactions have been surprisingly positive from players and fans. Players now have recourse against bad calls; fans find the challenge moments dramatic and fun. "Instead of having a human make calls, you'd have a clinical robot making the calls," Berube says. "But it's actually creating more drama, because a couple times a game now a player will say, 'You thought that was a strike? I think that was a ball.' And then everybody looks up at the scoreboard together, and fans go crazy when their team is right."

For umpires, however, the experience has been brutal. Retired umpires have expressed sympathy for active umpires, noting that several times a game, someone questions their judgment and then 30,000 people look at a giant scoreboard to see if they blew it. "If you blew it, everyone cheers," Berube says. "30,000 people are cheering for a mistake that you made."

The most dramatic example involves umpire CB Buckner, a 26-year veteran and one of the few Black umpires in baseball. In a game between the Cincinnati Reds and an unnamed opponent, Buckner called a third strike on a pitch that was clearly low. Reds third baseman Eugenio Suarez challenged, and the ABS showed the pitch was outside the zone. The call was overturned. Then it happened again on the very next pitch. Buckner had six calls overturned in that single game. The clip went viral, and Buckner became the subject of intense media scrutiny and social media mockery. "I did not know the name CB Buckner before this week," Berube says, "and now everybody in baseball knows who he is." To make matters worse, later that week Buckner was hit in the face by a foul tip and had to leave a game.

Berube notes the irony: when the original episode aired, he came out "softly on the side of robot umpires" because he thought it would help people see umpires as human beings by removing some of the vitriol. Instead, the challenge system has done the opposite. "It has put this person under a microscope," he says. "It has empowered people to yell at this guy and be mean to him on social media."

34:39Conclusion

This episode matters because it captures a moment of genuine transition in one of America's most tradition-bound institutions. The robot umpire story is not a simple tale of technology triumphing over human error; it is a nuanced exploration of what we actually want from sports, from work, and from each other. The ABS system is more accurate, but accuracy comes at the cost of the quirks, injustices, and human moments that make baseball feel alive. The challenge system, in its first week, has created new drama—but also new opportunities for public humiliation. The episode leaves listeners with an unsettled feeling: we wanted better calls, but we may not have fully considered what we were asking for.

Key Takeaways

• Major League Baseball umpires are about 94-97% accurate on balls and strikes, but the 34,000 bad calls per year can decide championships.
• The ABS (Automatic Balls and Strikes) system uses HD cameras and missile-tracking technology, not physical robots, to determine pitch location.
• The 2025 MLB rollout uses a challenge system, not full automation: human umpires make calls, but players can challenge up to two calls per game (retaining successful challenges).
• The system had to be reprogrammed to be *less* accurate, expanding the strike zone by about an inch to match what human umpires actually call.
• Human umpires unconsciously adjust the strike zone based on context (weather, score, pitcher performance)—a "compassionate umpire effect" that robots cannot replicate.
• The challenge system has created new drama for fans but has also led to intense public scrutiny and humiliation of umpires, exemplified by CB Buckner's six overturned calls in a single game.
• The episode's original hope—that robot umpires would reduce vitriol toward human umpires—has not been realized; instead, the technology has amplified criticism.