Robot Zone Could Make Receiver Defenses More Valuable Than Ever

To what extent does an ABS challenge system harm a catcher’s ability to throw the ball? This question has been running around in my head for a long time. I’ve been waiting for the offseason to really dig into the numbers, and, well, here we are. It’s the offseason. But now that I’ve dug through all the data I can find, I think the entire premise of this question may be flawed. I think correcting a few strike calls in a game would eliminate some good pitches. There is no doubt that this will hurt the better setters more than the worse setters because they gain more hits and have more to lose. At the same time, smaller framers will have more opportunities to challenge, increasing their numbers slightly. As a result, the gap between good and bad frames will shrink, furthering a trend that has been going on since we first gained the ability to quantify the value of pitch frames. It’s still valuable, just not as valuable as it once was. But I’m not so sure anymore. Let’s start with the data.

I pulled out frame data for all the major leagues I could. I pulled out all-league and individual catcher batting averages in and outside the strike zone in the majors and Triple-A, using the same challenge system in 2025 as in 2026. I can tell you that last season, 26 catchers got significant playing time in Triple-A and the majors, and their so-called hit rate on pitches in the major league shadow zone dropped an average of 1.4 percentage points within the zone and 1.7 percentage points outside of the minors. So while the strike zone may be tighter in Triple-A, the pitch framework in the majors is still harder. But the only data on how the challenge system will actually work in the minors and in 2025 spring training comes from MLB press releases, and it’s extremely sparse.

Of course, these data must exist. Baseball expert Tom Tango wrote a series of interesting points on his blog a month ago. As you’d expect, players are more likely to challenge calls in high-leverage moments, later in the game, and on pitches that determine at-bat outcomes. Therefore, they tend to be less successful in these situations. They question not because they’re convinced they’re right, but because they really want the call to go in the opposite direction. Tango also knocked out some catchers and hitters who were particularly good or bad at the challenge. Not only did he provide their statistics — poor Zach Veen challenged 24 pitches and only overturned three — but Tango also revealed that Savant will introduce a challenge probability number next year, using distance from the edge of the strike zone to calculate the likelihood that any given pitch will be challenged, and the likelihood that any given challenge will be successful. From there, it’s easy to calculate how much more challenge value each hitter or catcher creates than the average player.

All of these numbers will be very interesting. We’ll be able to see if a catcher who’s good at challenging behind the plate is also good at challenging in the batter’s box. We’ll see how relevant plate discipline and frame value are to making good challenge decisions. We’ll see if certain pitchers or certain types of pitching provide more of a challenge or have more success. We’ll be able to answer your questions about how it affects the value of the frame! There’s nothing to go on yet, though.

Here’s what we know so far. During spring training, 2.6 percent of all bat calls were challenged, with 4.4 percent coming from the offense and 1.8 percent from the defense. 80% of spring game challenges were five or fewer, and 52.2% of challenges were successful. Batters have a success rate of 50%, catchers 56%, and pitchers 41%. The last two numbers added together give the pitching staff an overall success rate of 54.4%. Aside from the pitchers’ numbers — which don’t really matter since they’ve proven to be so bad at challenging that they’re all but banned from doing so in the minors — all of those numbers are pretty close to 50%. In 2024, the Triple-A success rate is 50.6%. Understandably, the league has an incentive to emphasize this fact, promoting the notion that the challenge system won’t have much of an impact on the game because everything will be balanced. So we get this quote from MLB Executive Vice President of Baseball Operations Morgan Sword: “The rate was not much higher or lower than 50 percent in the strike zone, in any format that we tried, which is very interesting because these are the most ‘controversial’ subset of pitches among players.”

Still, these numbers don’t exactly balance out, so let’s see how they stack up in the regular season if they hold up. In 2025, Triple-A is averaging 4.2 challenges per game, which equates to a major league season total of 10,206 challenges. Assume the percentages we saw during spring training are exactly right. Batsmen initiated 59.1% of their challenges with a 50% success rate, while defenders initiated 40.9% of their challenges with a 54.4% success rate. In this case, the batter will win 3,015 challenges, while the defender will win 2,271 challenges. That’s a net result of 744 extra balls, which equates to about 93 extra runs. Remember, in the major leagues, umpires only called 236 at-bats on pitches outside the shadow zone all year. Correcting the worst mistakes is only a small part of the plan. In other words, the offense is going to be way ahead of the game, and much of that improvement has come at the expense of the field-makers.

I’m not so sure these numbers hold up, though. As many have pointed out, the Statcast zones are a bit tighter than those assigned by actual human umpires, which would lead to more strikes we would expect. I particularly doubt batsmen will continue to challenge at such a high rate. A Reddit user named Avondice posted some detailed breakdowns of the challenges for the 2025 AAA season. I contacted them and asked where they got this data from and they said it comes directly from Major League Baseball’s pitch-by-pitch data. The breakdown shows that the overall success rate is 49.5%, with the success rate of offensive challenges being 45.1% and the success rate of defensive challenges being 53.5%. With a little algebra, we can reverse engineer these numbers and figure out that 52.4% of challenges must come from defense, while 47.6% must come from offense. If these numbers hold up in the major leagues, the trend will be toward defense rather than offense. The end result will be 670 extra strikes, which equates to roughly 84 runs wiped out.

Again I’m not sure how much to trust this set of numbers. Whether it is spring training or Triple-A games, they are completely different from the major league regular season. As I wrote last week, major league umpires are more accurate than minor league umpires, even without challenging the system to correct some of their mistakes. They have far fewer big mistakes, and without those low-hanging fruit, the regular-season major league challenge will likely be much less successful than what we saw during spring training (when pitchers were wilder and umpires less accurate). Still, my point here is that even small differences can add up to a large number. As Sword said, these ratios are all far from 50%, but that doesn’t mean they don’t have a big impact.

Another important point is that if we put challenges into their own category, separate from the framework, then yes, the ABS challenge system will reduce the scope of the framework results. But we can just as easily think of the challenge system as part of the framework. This is still just one way to win strikes, and I’d like to remind you that framing isn’t just about stealing strikes on pitches outside the zone. Catchers are more concerned with “keeping strikes.” That is, ensuring that when their pitchers hit that zone, they are rewarded with a called strike. The best pitchers in the league strike on nearly 90 percent of shadow pitches inside that zone, but outside of that zone, that number is under 20 percent. The challenge system will further reinforce this focus, and I’d like to remind you that catchers flipped at a much higher rate than hitters in the two sample sets we broke down. Even though we sabermetric experts divide the leaderboard into one category for composition and another for challenge, receivers who excel at both will be more valuable than ever! (As for whether these two skills are related, the jury is still out on the little data we have so far. Tango notes that Harry Ford is the worst challenger and P.J. Higgins is the best. Neither player has looked like a great pitch-setter this season.)

We’re only going to talk about a few overturned calls in each game, and most of the time they’ll probably even out; both teams will get a call or two, the referees will yell less, and everyone will win. But that doesn’t mean the situation will be evened out between offense and defense. If hitters end up getting more value out of challenging the system, like they did during spring training, then catcher defense (a combination of frame and challenge results) could take a real hit. The distance between elite framers and poor framers is likely to shrink further. But if catchers get more out of the challenge system, those who can combine great framing with great challenge decision-making may be more valuable than ever, even if framing numbers take a hit.