The Hawk-Eye system will determine the validity of a checked swing based on whether the bat head is ahead of the knob by more than 45 degrees.

Teams can continue to challenge checked swings until they have one unsuccessful challenge.

Joe Martinez, MLB's vice president of baseball operations, stated that the goal is to evaluate the technology's effectiveness and explore its integration into gameplay.

Commissioner Rob Manfred indicated that regular-season implementation of this technology could occur in 2026, although it is not guaranteed.

Under the new rule, a swing will be defined by whether the bat crosses a line parallel to the foul lines at first and third base, providing clearer criteria for calls.

Currently, there is no formal definition of a checked swing in the Official Baseball Rules, leading to inconsistencies and criticism.

The Florida State League has a history of being a testing ground for MLB rules, having previously implemented the Automated Ball Strike (ABS) system.

On May 20, 2025, Major League Baseball (MLB) will begin testing a new technology system for challenging checked swing calls in the Class A Florida State League.

This initiative is part of MLB's broader strategy to enhance game accuracy, which may include the rollout of an automated balls and strikes system by 2026.

However, MLB emphasizes that this is a pilot program with no guarantee of future implementation beyond the initial testing phase.

Both the batting and defensive teams can make a challenge, with the outcome displayed on the ballpark video board.

Previously, umpires relied on subjective judgments regarding the hitter's wrist movement, which resulted in inconsistent calls.