What MLB should have done instead of the ABS challenge system

The 2020s have seen a number of significant tweaks to baseball’s playing rules, such as the pitch clock, restrictions on defensive shifts, and the automatic runner in extra innings. The 2026 season is bringing us another one—the Automatic Ball-Strike (ABS) challenge system, which gives batters, pitchers, and catchers the opportunity to challenge ball and strike calls a limited number of times in each game. Is this change a good one? Will it solve the problem that it’s trying to address, or would there have been a better way to tackle it? My take is that while the ABS challenge system is a marginal step forward in improving ball and strike calls, another approach could have advanced the improvement much further.

What is the ABS challenge system?

At the start of each game, each team is given two challenges. If a challenge leads to a successful overturn of the call, the team retains it; if not, the team loses that challenge. If the team loses both of its challenges, it can no longer challenge the call unless the game goes to extra innings. In an extra inning game, each team that has lost its challenges will be awarded one additional challenge at the beginning of each extra inning. The only players allowed to challenge the call are the batter, the pitcher, and the catcher. They must request the challenge (by tapping on the cap or helmet) immediately after the call is made and are not allowed to receive assistance from the dugout or other players.

When the call is challenged, a visual graphic of the pitch’s location relative to the strike zone will be shown on the scoreboard. The data come from MLB’s Hawk-Eye camera technology, which has been deployed in all MLB ballparks since 2020. Each challenge takes about on average 14 seconds to resolve, so with an average of four challenges per game, the net effect will be to add about one minute to the length of each game.

During spring training, the success rate on challenges was between 50 to 60 percent, so we expect that a large share of challenges will be unsuccessful.

To implement the technology, the strike zone has been redefined in a way that allows for more precision. Instead of the traditional three-dimensional strike zone that has been used in the past, the new strike zone is a two-dimensional rectangle crossing the midpoint of home plate, which is 17 inches in width (matching the plate), with the top and bottom of the zone calculated as 53.5% and 27% of each batter’s measured height. The strike zone does not vary if a player crouches or adjusts his stance.

Needless to say, there will be a whole new set of strategies associated with the ABS challenge system. The baseball analyst known as Tangotiger has analyzed the math associated with a team optimizing its use of the challenges and finds, for example, that challenges are best used when the count is three balls or two strikes, or when there are runners on base. In addition, catchers will now have to help their pitchers understand how the strike zone varies with each batter’s height, since the traditional visual cues of the batter’s knees and chest may not work well for some batters.

Automatic balls and strikes are good

In the 2025 season, MLB umpires made, on average, 11 mistakes per game in calling balls and strikes, mistakes that affected the performance of batters and pitchers and occasionally tipped the balance of a game from one team to another. While there were sometimes complaints about the accuracy of the old Pitchf/x system that MLB used to use for tracking pitches until 2016, the new technology is extraordinarily accurate. With the adoption of the ABS challenge system, MLB has decided that the calls made by the ABS technology are superior to those made by umpires, and I agree with that decision.

Why didn’t MLB adopt a fully automated ABS system?

MLB has conducted several years of testing of ABS, beginning with the independent Atlantic League in 2019. Since 2023, it has been tested in Triple-A leagues. When those tests began, two systems were compared: a fully automated ABS system was used for games played on Tuesday through Thursday, and the ABS challenge system was used for games played on Friday through Sunday. After a season and a half, MLB announced that it would stop testing the fully automated ABS system but would continue testing the challenge system, citing “a clear preference among fans, players, managers and other personnel for the Challenge System.”

As far as I can tell, MLB has not published its detailed analysis of the comparison of the two systems, but we can piece together some information from articles by reporters who were covering these developments, such as Jayson Stark of The Athletic. A large majority of players (61 percent) preferred the challenge system versus 11 percent who preferred the fully automated system. Players cited three main reasons for disliking the fully automated system:

1. Game pace was slowed. Two reasons why the fully automated ABS system might slow the pace of play were cited. First, the fully automated system slightly increased the number of walks, which led to longer games. But this conclusion seems like it might be questionable, because while the two systems were being compared, MLB was also testing a slightly smaller strike zone (the top of the zone was a couple of inches lower), which would have led to more walks. Since then, the height of the strike zone has been tweaked to make it more similar to the previous strike zone, so it’s not clear that the additional walks would still happen. (I’d also argue that with on-base percentages currently near their lowest levels in the last 50 years, it wouldn’t be terrible if a few extra batters drew walks.) Probably the bigger concern for most players with pace of play, though, is a slight delay of about two seconds for the umpire to be informed whether the pitch was a ball or a strike. That delay added maybe three minutes to the length of each fully automated game (versus maybe one minute added to each challenge-system game), and of course players and fans would prefer not to wait to find out those calls.
2. Framing skills became irrelevant. All modern catchers have spent many hours working on their framing of pitches, but the fully automated system cares only about the location of the pitches, so framing was no longer relevant. So, it’s understandable that most catchers, and presumably some pitchers as well, would not be happy with the loss of the ability to “steal a strike” (that is, convince the umpire to call a strike on what would have been a ball) through framing.
3. The new strike zone definition seemed uncomfortable. This objection is complicated because, as I’ve noted, the experiment coincided with MLB testing a slightly smaller strike zone, so it’s unclear how much of the discomfort was due to the smaller strike zone. The ABS strike zone has now been adjusted to more closely match the traditional zone, but we know that there are still small systematic differences between the zones called by umpires and the zone called by ABS—in particular, umpires tend to round out the corners of the strike zone, giving the zone a slightly oval shape, rather than following the strict rectangle used by ABS.

The fans also expressed a preference for the challenge system, though their margin of preference was not as large as that expressed by the players. I didn’t see any reports of the reasons given by fans for their preference, but reasons # 2 and 3 above seem specific to players, so I suspect that the fan preferences were mainly driven by pace of play. Also, fans seem to enjoy the drama of seeing the outcome of the challenge shown on the scoreboard. I would assume that only fans in attendance at games were surveyed, whereas the majority of the audience for MLB is watching televised games.

Framing doesn’t enhance the fan experience

In considering making changes to baseball rules, I believe the primary focus should be on enhancing the fan experience of the game, as it is the customer base that funds the sport and keeps it running. Player preferences can be considered to the extent that they are supporting goals that are good for the sport, such as keeping the players healthy, and do not reduce the enjoyment experienced by the fans.

Catcher framing is clearly a valuable and important skill in modern baseball. But it is a skill that is largely invisible to most fans and therefore does not enhance the experience of the sport for most fans. Even the catcher who is the best framer in baseball (probably Patrick Bailey right now) is stealing (relative to the average catcher) just one additional strike per game. Over a season, those extra strikes add up, so that over the course of a season his framing helps his team prevent 20 to 25 opponent runs from scoring, which is worth 2 to 2.5 wins. That contribution to defense is comparable to that provided by the best defensive shortstops or center fielders in baseball, but framing never makes the highlight reels. The motions associated with framing are so subtle that probably only a few dozen fans at the ballpark, those seated in the expensive seats directly behind home plate, would have any hope of seeing them; and then only if they were paying very close attention.

Watching a televised game, an attentive fan is better positioned to see framing, but it is still subtle, and because all catchers are trying to frame pitches, it is hard to see the movements that make one catcher better than another. Furthermore, that extra strike that is “stolen” in each game is not directly identifiable. We can only say that it is happening by looking at the statistics as they accumulate, but because it is measured relative to the “average” catcher who is also trying to steal strikes, we can’t tell with certainty whether any particular strike wouldn’t have been stolen by an average catcher. So, there is no applause or replay happening when the strike is stolen.

I believe that fans enjoy watching baseball largely because of the athletic skills that the players exhibit during the game—hitting, throwing, running, sliding and so forth. Framing is not one of those skills. And I believe that the current emphasis on framing reduces, at least to some extent, the other athletic skills of catchers that are more enjoyable to watch. Even if the one-knee-down catching style that is used to help with framing doesn’t hurt catchers’ ability to block pitches, throw out base stealers or field bunts, the general selection of catchers for their framing ability rather than their other defensive skills surely must deemphasize those other skills. Furthermore, the selection of catchers for framing ability surely prevents some catchers who are good hitters but poor framers from reaching an MLB roster.

A plan for a (nearly) fully automated ABS that (mostly) maintains the pace of play

First, let me emphasize that this idea is not entirely original to me. Joe Posnanski recently wrote about an idea that Bill James came up with. Unfortunately, I believe that Bill’s website has now disappeared, so I wasn’t able to track down a link to the original source. But I’ve taken Joe’s description of it and added some tweaks that I think can help address the pace of play issues that players objected to.

The idea is that all home-plate umpires would wear an earpiece that prompts them after a pitch whether the ABS system says it’s a ball or a strike. The umpires would still make the calls—if they think the ABS system got it wrong, they are free to overrule it. If it takes a second or two for the prompt to arrive and they are certain that the pitch was a ball or a strike, they will be told they should make the call immediately. But if a pitch is close to the boundary of the zone, MLB will recommend that they wait up to a couple of seconds for the prompt to arrive before making the call. So, if the pitch is in the heart of the plate, it’s immediately called a strike; if it’s four inches off the plate, it’s immediately called a ball. If it’s near the boundary, the umpire will wait a second or two to get the prompt, then make his decision taking account of what the prompt says (possibly overruling the prompt, but I’m guessing in most cases going along with the ABS prompt). If there’s a glitch in the system and the prompt doesn’t arrive within a couple of seconds, the umpire goes ahead and makes the call without waiting longer.

I’d guess that 70 to 80 percent of calls would be made immediately. There will still be some wrong calls—umpires occasionally get confused and call pitches in the heart of the plate as balls, or pitches three or four inches out of the zone as strikes. But those kinds of mistakes are rare, and assuming most umpires don’t overrule the ABS prompt very often, my guess is we’re talking one or two missed calls per game, rather than an average of 11 per game under the current system. That’s infrequent enough that catchers will lose the incentive to frame pitches, but as I’ve already discussed, I’m fine with that. Delays of one or two seconds on maybe 20 to 35 calls per game would add only a minute to the overall game time, similar to the challenge system. And unlike under the challenge system, almost all of the ball-strike calls will be correct. If the system makes it slightly easier for a batter to draw a walk, I’m fine with that.

If we’re still worried about missed calls, we could perhaps give each team one challenge per game. My guess is that they would mostly be saved for fixing the rare egregious mistakes.

I’ll add one additional suggestion. My guess is that if MLB is willing to invest in technology, there would be ways to speed up the processing and communication of the prompts to the umpires, with the objective of giving them the prompts in less than one second. I’m not an expert on this technology, but I do know that Wall Street firms have invested in technology that allows them to process newly arrived economic data and communicate it for trades in milliseconds, so it suggests to me that such technology is probably available with some investment.

Why the ABS challenge system may be leading us in the wrong direction

While the ABS challenge system does allow teams to correct some bad ball and strike calls, and thus is modestly better than the current system, my concern is that it is likely to stall further progress on improving these calls. It will change the discussion from, “Wow, I can’t believe how badly the umpire messed up that call” to “Why did our team waste our challenges when we really needed one at the end of the game?” That is, the focus will inevitably shift from the decisions of the umpires in making the calls to the decisions of the players in deciding when and how to use the challenges.

I expect that will leave us in an equilibrium where umpires continue to miss eight or nine calls per game, catchers continue focus on framing, and there is very little incentive or desire to move toward a less error-prone system. And if that’s where we end up, I think it will be regrettable.