Rules and System
What ABS Is and How It Works
A direct explanation of MLB's ABS challenge system, the technology behind it, and how I mirror that system inside AiBS.
ByColby Reichenbach
MLB uses an ABS challenge system, not full automated strike calling, and the distinction matters.
In MLB's current format, the plate umpire still calls the pitch. ABS only enters when the pitcher, catcher, or batter immediately challenges that call. The tracking system then confirms or overturns the pitch in real time.
That operational detail matters because I am not trying to explain an abstract strike zone in isolation. I am explaining a challenge system with strategy, resource constraints, timing rules, and a specific technical implementation.
I mirror that system directly in AiBS. I model the rule set, the geometry, and the baseball state change that follows from a confirmed or overturned call.
League rules
The challenge system is narrow on purpose.
MLB gives each team two challenges in a nine-inning game. Teams keep a challenge if it is successful and lose it if it is not. In extra innings, a team that has none remaining is awarded one. The challenge must come from the pitcher, catcher, or batter, and it has to happen right after the pitch. The dugout is not supposed to drive the decision.
Those rules create the strategic layer that makes ABS interesting. A challenge is a resource, not just a complaint. The baseball question is not only whether a call was wrong. It is also whether a team used a limited correction opportunity well.
- •Each team starts with two challenges.
- •Successful challenges are retained; failed challenges are lost.
- •Only the pitcher, catcher, or batter can challenge.
- •The request must be immediate.
- •A team with no challenges left gets one in extra innings.
Technology and geometry
The system is geometric, but it is not vague.
According to MLB, the challenge system runs on Hawk-Eye tracking with 12 cameras in each park. The ABS zone is a two-dimensional plane centered over the plate. It spans the full 17-inch width of home plate, and its top and bottom are scaled to the batter's measured height. The top is 53.5% of player height and the bottom is 27%. Pitch location is measured at the midpoint between the front and back of the plate, and any part of the ball clipping the zone counts as a strike.
I mirror that framing in AiBS as closely as the data and public baseball feeds allow. The geometry layer is direction-aware, which means I treat a called strike that should become a ball differently from a called ball that should become a strike. That difference matters because the baseball implication is different, the count change is different, and the modeled value is different.
Zone width
17 in
Top bound
53.5% of player height
Bottom bound
27% of player height
Tracking source
12-camera Hawk-Eye system
How I model it
I model ABS as a baseball event, not just as a location check.
I do not stop at whether the pitch should have been a strike or a ball. I also track who challenged, what count changed, whether the challenge was retained, and what baseball state followed from the corrected call.
That design choice is why the rest of the product can move from simple call correction into timing, value, and pressure. ABS is a rules-and-decision system built around pitch calls, so the geometry matters, but so do the count, the inning, the score, the base state, and the number of challenges remaining.