Rules Explainer
What ABS Actually Is
A plain-language explanation of MLB's current ABS challenge system and the geometry rules AiBS is trying to mirror.
ByColby Reichenbach
Overview
MLB's current ABS implementation is a challenge system, not full robot umpiring.
ABS in the majors means the plate umpire still calls balls and strikes, but the pitcher, catcher, or batter can immediately challenge a call and send it to the tracking system for a correction.
That distinction matters because the product logic needs to mirror the league's actual operational system, not just the abstract rulebook strike-zone language. AiBS therefore models challenge outcomes around the current challenge format, batter-specific zone bounds, and MLB's published ABS strike-zone framing.
The public version of the product is designed around that reality: MLB chose a correction system with strategic constraints, not a computer that replaces the plate umpire on every pitch.
On-field process
The review is immediate and intentionally narrow.
MLB's current system is built for fast correction. The challenge has to come from the pitcher, catcher, or batter immediately after the call. Teams retain successful challenges and lose unsuccessful ones. The point is to create a correction mechanism without turning every plate appearance into a manager-driven replay workflow.
That strategic layer matters to AiBS because challenge usage is not just about correctness. It is also about timing, leverage, and resource management.
Geometry
AiBS is aligned to current ABS logic, not a vague zone approximation.
The product uses batter-specific strike-zone resolution and direction-aware inside/outside geometry for challenge analysis. The model layer is aligned to MLB's published ABS framing rather than a generic stat-zone approximation.
That means the product distinguishes between called strikes that should become balls and called balls that should become strikes, instead of treating all distance from the boundary the same way.