Home Plate Umpire Brian Walsh uses an earpiece to hear the electronic notification as to weather a pitch was a ball or a strike by the ABS system during a AAA minor league baseball game.Image: Rich Schultz/Getty Images ShareIf theres one thing baseball fans are averse to, its change. Over the MLBs 149-year history, alterations to the games rules, like lowering the pitchers mound (1968) or introducing instant replay challenges (2014) came only after years of heated debate between reformers and purists. Maybe the most contentious issue ever to divide these two camps is whether or not to replace notoriously inaccurate human home plate umpires with less fallible machines. Though that was once largely considered out of the bounds of possibility, MLB games officiated by so-called robot umpires are now closer to reality than ever before.Starting this week, batters stepping up to the plate during spring training games will have the ability to challenge an umpires pitch calls and have them immediately reviewed by a computer. A human official will still stand behind the plate calling balls and strikes for the whole game, but the so-called robot umpire, powered by a computer vision system called Hawk-Eye, will be tracking the location of every pitch. Players from both teams will each have two opportunities or challenges per game to contest the human call with the machine. Though this hybrid umpire system wont make its way to regular season major league games in 2025, player and fan reactions during this crucial trial period could determine whether or not it becomes a regular staple in games. Ready or not, robot umpires are here.One of over 30 ABS cameras monitor each pitch for balls and strikes during a AAA minor league baseball game between the Memphis Redbirds and Lehigh Valley IronPigs. Image: Rich Schultz/Getty Images Rich SchultzWhy do some players want automated calls?Anyone whos watched baseball on television in recent years will be familiar with the faint, rectangular box that appears in front of the batter. Thats the strike zone. While nobody on the field can actually physically see said zone, it does have precise, measurable dimensions that vary from batter to batter. (In general, the strike zone is the width of the home plate and the area in height between a batters shoulders and the bottom of their knees). Home plate umpires tasked with calling balls and strikes know the strike zone parameters in theory, but they often fall short of making perfect calls because, well, theyre human. Past research has shown that on aggregate, human umpire strike zones end up looking less like the desired rectangle, and more like an oval. 100-mile-per-hour fastballs and quickly plummeting curveballs arent the easiest things to judge correctly every time.Thats where Hawk-Eye comes in. First implemented during televised cricket games in 2001, the system uses specially designed cameras to track a balls trajectory from multiple angles. That is then immediately fed into a computer vision algorithm that determines its final location. While it isnt mathematically perfect, its far more accurate over time than the human eye. Hawk-Eye systems are already implemented at most professional tennis tournaments and have even led to the removal of human line judges in three of the sports four biggest tournaments. The National Football League (NFL) also started using Hawk-Eye during the 2021-2022 season for certain instant replay reviews. The MLB began using the same technology for video replay of certain calls in 2014, but not for balls and strikes.How will the robot umpire work during gamesThe pitch review system being trialed during spring training formally called Automated Ball-Strike System (ABS), is attempting to find a middle ground between all human and all machine pitch calls. Hawk-Eye is working behind the scenes tracking every pitch, but teams will only be able to call on it twice per game as a challenge to the home plate umpire. This strategic use of replays is similar to the way challenges already work in the sport for other reviewable calls like home runs and plays at bases.Unlike that prior system though, ABS challenges can only be requested by the hitter, pitcher, or catcher. To signal a challenge, the player will tap the top of their hat (or helmet in the batters case). From there, a graphic showing Hawk-Eyes call will appear on the main video board for everyone in attendance, players and fans alike, to see in real-time. A team only loses one of its challenges if the umpires initial call is correct. So, in theory, a team could challenge balls and strikes more than twice per game. The clip below shows an example of how this challenge was used to overturn a strike-out call.This is a pretty big decision for the game of baseballthat we want to get everybody to weigh in on, MLB Executive Vice President of Baseball Operations Morgan Sword said in a recent MLB.com blog post,The ABS system, according to the MLB, will be in place at roughly 60% of spring training games this year, which means every team will have the opportunity to experiment with it at least once. Spring training officially kicked off this week and goes through the start of the regular season on March 27. But this isnt the first robot umpires have been used in professional baseball. The league began experimenting with ABS for all balls and strikes (full ABS) during Triple-A minor league games starting in 2019. That full ABS system quickly led to an increase in walks, and in turn, made games take longer. The MLB says the more limited challenge system was implemented based on feedback from those trials.Unsurprisingly, players and coaches arent all on the same page about whether robot umpires in the Big Leagues is a good idea. In an interview with The Rockies Insider this week, Colorado Rockies manager Bud Black spoke positively of the system, saying it adds another element for fan engagement.It adds another element for the fan experience to get involved, Black said.Theres an allure to it, he added. I think is a good thing.In a recent interview with The Athletic, Los Angeles Dodgers pitcher Tyler Glasnow, who himself used the challenge system while playing in Triple-A, reiterated that optimism. He even went as far as to call the challenges the most fun part of the game. At the same, others are worried some players may be too quick to use the challenges. In that same Athletic report, Morgan Ensberg, the manager of Triple-A team the Durham Bulls, said catchers were potentially wasting challenges on balls they thought should be called strikes. Dodgers first baseman Freddie Freeman similarly worried some teammates might flippantly request a challenge that would be better spent on a more important, game-critical pitch.I mean, I probably wouldnt even do it [challenge a call], Freeman told The Athletic. But we have a couple of guys that I would be worried that theyd just challenge every (pitch), that every strike call would be challenged and were going to run out in the first inning.Even if players are on the fence, polling shows baseball fans might be warming up to the idea of robot umpires. A 2022 Morning Consult survey found that 48 percent of self-described baseball fans said they supported the implementation of machines capable of automatically calling balls and strikes, compared to just 32 percent who opposed the idea.Baseball is trying to maintain its popularity by modernizingThe ABS system is part of a broader, years-long effort by the MLB to modernize a game steeped in tradition. That historical resistance to technological change has given the sport staying power, but it has also dealt a blow to its popularity. Just 10 percent of US adults surveyed by Gallup last year listed baseball as their favorite sport. Thats down from a high of 39 percent in the 1940s. Analysts have attributed that decline, in part, to the drawn-out length of games compared to more condensed sports like football and basketball. The MLBs recent introduction of a pitch clock in 2023 and limited mound visits in 2018 were both efforts to try and cut down the overall length of games. ABS challenges could similarly cut down on the amount of time batters, pitchers, and catchers spend bickering with umpires over various borderline pitches.And aside from making more accurate calls, the challenge system, as Black of the Rockies noted, has the potential to add the benefit of introducing a degree of excitement and fan involvement during more moments of the game. If the long track record of Hawk-Eye used during tennis matches is a guide, fans are more than willing to ooh and ahh in excitement at a digital representation of a ball on a giant screen.