When the officials wronged Serena Williams at the 2004 U.S. Open quarterfinals, permanent alterations came to professional tennis.

On that September night in 2004, onlookers at the National Tennis Center were baffled as Williams, in the decisive third set of a loss to Jennifer Capriati, was the victim of four questionable calls -- or what many would deem outright mistakes -- by the line judges and chair umpire. One ruling on a ball well inside the line was so egregiously incorrect that Williams received a call of apology the next day from United States Tennis Association president Arlen Kantarian.

“Hawk-Eye please," commentator John McEnroe said at one point during the match. "This is getting ridiculous.”

Shortly thereafter, Hawk-Eye arrived.

All these years later, tennis fans are quite familiar with the line-calling technology created by U.K.-based Hawk-Eye Innovations. It had been in use on television broadcasts for several years before Williams’ controversial loss, but that particular match sparked movement by the USTA, the International Tennis Federation and the Association of Tennis Professionals to sign off on widespread use of the Hawk-Eye system to allow players to challenge line calls they deem to be incorrect.

Hawk-Eye is now used at three of the sport’s four Grand Slam events -- the lone exception being the French Open, which is played on a clay court.

“Its job,” Hawk-Eye founder Paul Hawkins said, “is to let the sport do the talking and keep the officiant out of it. There’s nothing in any sport where 100 percent of everybody thinks it’s a good idea. But in tennis, it’s been fairly unanimously well received.”

In tennis, players can challenge in or out calls they deem to be incorrect. The Hawk-Eye-powered replay is summoned instantaneously, the original call either stands or is overruled and the game goes on.

What would such a challenge system look like in baseball?

We got an idea on Saturday night.

During a special MLB Network broadcast of the game between the Triple-A Charlotte Knights and the Syracuse Mets, three experimental Minor League rules were in place -- a pitch clock, larger bases and an automated ball-strike (ABS) challenge system.

The pitch clock -- and its impact on pace and game times -- has been the source of a lot of discussion this season, while the larger bases are a more subtle change aimed primarily at player safety (with some impact on the stolen-base success rate).

But the ABS challenge system is worthy of our attention, too. Because while no plans are in place to use it -- or ABS, in general -- at the Major League level in 2023, it has generated serious interest within the industry.

“If you ask the players and coaches who have had some experience with all these different options,” says an industry source, “generally they prefer the challenge format to what we call ‘full ABS’ and to having nothing.”

Let’s discuss the challenge system and why it might be beneficial for MLB.

1. How the challenge system differs from “robot umps”

“Full ABS” is what many refer to as “robot umps” -- a system in which the home-plate umpires are not making ball-strike decisions on their own, but rather, immediately relaying the Hawk-Eye system’s determination of ball or strike (which they receive via an earpiece). In 2022, full ABS has been in use at the Triple-A level.

As an alternative, the challenge system is akin to what is used in tennis. Umpires make the ball-and-strike calls, and pitchers, catchers and batters have the ability to make an appeal to the ABS system.

The challenge system has been in place at most venues in the Florida State League (FSL) throughout 2022 and, more recently, at Triple-A Charlotte. Each team gets three challenges per game, with successful challenges retained for future use in the game.

“It still gives the umpires the ability to call their strike zone so they’re not just back there listening to the earpiece,” says Andrew Graham, manager of Single-A Lakeland in the FSL. “But it also gives the players a better understanding of the strikes, so they can’t just randomly challenge a call in a situation. They have to understand we only get three challenges, so it really makes them concentrate more on the strike zone and track the pitches better. So it’s a great strategy.”

As with tennis, the challenge system operates quickly. The umpire, equipped with the earpiece, can immediately relay Hawk-Eye’s read of the pitch. If the facility’s technology permits (as it certainly would at the big-league level), the Hawk-Eye view can be shown to the fans in attendance via the video board (and, of course, to fans watching the broadcast, as well).

2. Why the challenge system might be a happy medium

Baseball, of course, has a long history of, um, differences of opinion on balls and strikes between its umpires and its players, managers and coaches.

In a game earlier this year, the Phillies’ Kyle Schwarber had a particularly epic meltdown when home-plate umpire Angel Hernandez rung him up with a called strike on a pitch that was outside the strike zone. Every time an obvious mistake like that occurs, there is a chorus of folks calling for “robot umps now!”

But it seems that, for every proponent of the bots, there is someone else who wants baseball’s so-called “human element” to be retained.

The ABS challenge system could be a happy medium between the two worlds. It provides an avenue by which glaring calls in big situations can be challenged without totally removing the nuances of umpiring that many inside the game still respect and wish to retain.

“I think good umpires have a really good feel for the game,” veteran Cleveland Guardians manager Terry Francona said. “They understand when it’s 10-0 or when a pitcher is locating. I think a pitcher that’s locating, when he’s following that [catcher’s] glove around, it should be easy for the umpire to kind of follow with you.”

Speaking of the catcher’s glove, the challenge system retains most of the value of pitch framing -- a skill that has been a focal point of catcher development and acquisitions in recent years.

As for the human umpiring element, for generations, 0-2 pitches in blowout games haven’t necessarily been called the same as 0-2 pitches in one-run games in the bottom of the ninth. Argue with that, if you will, but that is the culture that baseball people are accustomed to. So a fixed, unimpeachable and dispassionate standard set by a computer would make for a major adjustment.

The challenge system, on the other hand, is a more subtle solution that swoops in for the big moments.

3. How the challenge system adds some spice

When a close pitch happens in a game with the challenge system, drama ensues.

“Now,” says Morgan Sword, MLB’s executive vice president of baseball operations, “there’s a decision to be made.”

If it’s a close called strike, does the batter challenge? If it’s a close called ball, does the pitcher or catcher challenge? Those players are alone in their decision-making, because the manager, coaches and the players at other positions do not have the ability to challenge a call.

So with only three challenges per team, those with the ability to challenge must choose wisely.

“There’s a social pressure on the player to be confident that he’s right,” Sword says. “And then, if you don’t challenge, it takes the wind out of your sails as far as screaming at the umpire is concerned. I think it’s adding an entertainment element while correcting the pitches you most want corrected.”

Not everybody is sure that putting this pressure on players is a good idea.

“If you have three or four challenges a game, and your leadoff hitter takes two of them, I don’t think I’d be a big fan of that,” Francona says. “Just think of all the pettiness that can come from that.”

Some teams in the FSL have tried to get ahead of the issue by establishing guidelines, such as not permitting players to challenge 0-0 pitches or pitches before the fifth inning. Maintaining at least one challenge for a high-leverage moment late in close games is a must.

Ultimately, the challenge system becomes yet another strategic element of the game.

4. Umpires are correct more than you might think

At last check, players in Minor League games using the challenge system have only been successful on about 44% of challenges. In other words, the umpire’s call is actually right more than 55% of the time when a pitch is challenged.

Pitchers and catchers (46%) have fared a little bit better than batters (42%) when challenging.

Some teams have a “kangaroo court” that docks players who use a challenge incorrectly -- a competitive way of imparting lessons.

“Every hitters’ meeting we have the next day, we will remind the guys and we playfully show which pitches were challenged,” Graham says. “If it's on the edge of the plate, just on the black, then it might be a good challenge -- but still, there was no one on base and it was for a first-strike call, not for a third-strike call. We had a bad one where one of our players challenged a get-me-over curveball, first pitch, right in the heart of the plate, and he thought it was a ball. So there are bad ways to challenge. That will be spoken about in the hitters’ meeting. But we do it lightly, and they take it well.”

All told, games with the challenge system have featured, on average, 6.4 challenges, or 3.2 per team.

5. When might we see the challenge system in MLB?

Though Hawk-Eye’s tennis-ball-tracking technology was deemed suitable for use in tennis tournaments in 2005, it took a long time for baseball-tracking technology to be deemed suitable for experimentation at the professional level. MLB first dabbled with ABS as part of a partnership with the independent Atlantic League in 2019. (A detailed look at how the system was designed can be found here.)

The COVID-19 pandemic prevented further study in 2020, but the experiment continued in the Florida State League in 2021 and, as explained above, at certain Minor League venues in 2022.

While the results of the system have been positive, Commissioner Rob Manfred told reporters at the owners meetings in June that ABS was not expected to be brought before the league’s new Joint Competition Committee for potential use in 2023.

“There are difficult issues surrounding the strike zone that affect outcomes on the field,” said Manfred, “and we need to make sure we understand those before we jump off that bridge.”

But Hawk-Eye’s technology, which became the backbone of Statcast’s pitch-, hit- and player-tracking in 2020, has evolved enough to merit more serious consideration soon, perhaps as early as 2024.

“I can assure baseball fans,” Hawkins said, “that having been involved in 25 different sports, MLB has been very thorough in their research and analysis of what is the best way of doing it.”

Interestingly, Hawk-Eye originated with the sport that is often cited as an early form of baseball -- cricket.

In 1999, Hawkins was a British Ph.D. student in artificial intelligence and a semiprofessional cricket player. He had a bad call go against him in an important match and stewed about it, then set about to develop a system that could correct the bad calls. It started off as a television enhancement, then eventually (with the help of that famous Williams-Capriati match) became an officiating enhancement.

As in tennis, Hawk-Eye provides the backbone of a challenge system in international cricket events. If a team disagrees with a leg-before-wicket decision, the system can be summoned to view both the actual and projected flight of the ball.

“The only problem is whatever [number of challenges] you limit it to, there’s always a chance you run out of challenges,” Hawkins says. “That happened to Australia in cricket recently, and how did the press react? Well, the umpire didn’t get a great deal of bad press, because the reaction was the Australians shouldn’t have used their challenges on the other calls. Their destiny was in their hands.”

A challenge system put destiny in the hands of cricket players. And it put destiny in the hands of tennis players.

Baseball players just might be on deck.