SCOTTSDALE, Ariz. -- It’s one of the boldest experiments in the history of the Arizona Fall League. Whether it goes from the “laboratory” to the Major Leagues remains to be seen, but there’s no question the use of “robo-umpires” at Salt River Fields this season generated conversation among players and coaches.

The automated ball-strike system (ABS), as it is formally called, was used to call balls and strikes at all games at Salt River Fields, the home for both the Salt River Rafters and the Scottsdale Scorpions. The system was used during the 2019 regular season in the independent Atlantic League as part of a partnership with Major League Baseball. The pitch tracking system at the ballpark reads the pitch, then software determines whether the pitch crossed through any part of the strike zone, which adjusts to the height of each player. A ball or strike audio signal is sent to the home-plate umpire, who then makes the call accordingly.

Now that we have a full AFL season under our belts with the use of ABS, there is a reasonable sample size from which to gather some feedback, something MLB will certainly take into account when next steps are considered.

“Inside and outside pitches are pretty well done,” said Twins top prospect Royce Lewis, who played the fall season for Salt River. “I think up and down is the only part where they’re trying to figure it out. A curveball might break at the top late and catch the top part of the zone. It also might break early and catch the bottom part of zone. I think that’s some of the things that need adjusting. I’m sure someone’s smart enough to figure that out, just not me. I’m sure it’ll be figured out soon.”

Lewis’s comment echoes a sentiment heard from numerous people we spoke to. Curves that clip the top or bottom of the zone haven’t traditionally been called strikes by umpires, especially if they end up in the dirt, but they are technically strikes by the rule book. Players and fans saw this dynamic come into play when Giants outfield prospect Jacob Heyward, the younger brother of Cubs outfielder Jason Heyward, got ejected after voicing his displeasure about a called third strike from ABS.

“It’s very different, especially being a catcher,” Glendale Desert Dogs backstop Tyler Stephenson (Reds) said. “I think the biggest change, a bunch of people have said, is the up and down calls. We’re so used to the ‘normal strike zone.’ Especially some of those breaking balls, I’m sure people have seen the videos, those 12-to-6 breaking balls that just clip the bottom of the zone.”

As you can see in the clip of Heyward’s strikeout and ejection, the pitch was almost in the dirt, and is not the kind of offering that would traditionally be called a strike. However, as the graphic below shows, it appears to have been a devastating curveball that clipped the lower inside corner of the strike zone.

Heyward wasn’t the only player to take issue with the “robo-ump” this year. In one of the first games of the season, D-backs shortstop prospect Geraldo Perdomo had words for the home-plate umpire and then gestured up to the booth after the umpire pointed to his ear and reminded Perdomo it wasn't him who was making the call.

“It’s a little different for sure, and some of us get frustrated with it and you see some people point up to the top of the media booth up there,” Lewis said. “You don’t have anyone to argue with, so it’s different. Taking the human nature out of the game is a lot different, so everyone is kind of adjusting.”

More than anything, players agreed, using the system requires them to adjust to the way they’ve always done things.

“It seems like sometimes it’ll give you a little more on the corner than usual, but I think it’s just kind of in your head,” said Rays pitcher Shane Baz, who pitched largely out of the Salt River bullpen. “It’d be a really big change in baseball. It’s just something you have to adapt to, I guess.”

Adapting to rule changes is nothing new for MLB players. In fact, they have proven to be quite adept at adapting. As much of an adjustment as it seems like it would take should the ABS be used in Major League games, recent history suggests that would adjust pretty quickly. For example, much was made of the “Buster Posey rule,” to avoid collisions at the plate, as well as the elimination of the neighborhood play and the ability to break up double plays at second, but players moved on quickly after those rules were adopted in recent years.

Major League Baseball will also adapt based on feedback received during this experiment, which has been perceived as largely successful, with the technology working well. One thing to be discussed is where to set the strike zone on the system so it will most fairly call balls and strikes. During the Fall League season, the zone was set from the hollow of the knee to 4 1/2 inches above the belt, which is in line with the strike zone as defined in the MLB rule book: “The strike zone is that area over home plate, the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the hollow beneath the kneecap.”

But since there have been a number of questions raised due to those settings, it’s possible that would change before the system is used any further.

“With that zone, I think they are technically strikes or they’re clipping the zone, but as far as human nature … an umpire that’s human would realize that’s not a hittable pitch for someone that’s throwing 98 and has a breaker at 80, like Justin Verlander, or someone that’s just unhittable, and that wouldn’t be fair to the hitters,” Lewis said. “I think with the robo-ump, that’s the only part they can’t distinguish yet. Whatever they do, I’m sure it’ll be better.”

One of the biggest adjustments will come with pitches that aren’t executed as desired. Often, if a catcher sets up one way but the pitcher misses his spot, the pitch is called a ball, even if it is in the strike zone. The ABS would end that, much to the chagrin of hitters.

“The biggest thing is, as a hitter, you kind of get a feel for how pitchers are attacking you,” said Salt River manager Keith Johnson, who managed the Triple-A New Orleans Baby Cakes in the Marlins organization during the 2019 season. “For the most part, it’s up to them to execute their pitches. That kind of allows a guy to not necessarily execute a pitch. It could be an 0-2 count, they try to go fastball in, so the catcher sets up and the catcher reaches all the way over here and it clips the outside part of the zone, and now it’s a strike.”

They say baseball is a game of adjustments, so all of this fits right in.