Major League Baseball is introducing a new technology-driven system to adjudicate checked swing calls in the Class A Florida State League, beginning tonight. This pilot program uses the Hawk-Eye bat-tracking system—previously tested in the Arizona Fall League—to bring clarity and consistency to one of baseball’s most debated judgment calls.

The Hawk-Eye system determines whether a swing occurred by measuring if the head of the bat moves more than 45 degrees ahead of the knob. This angle corresponds to the baselines: for right-handed hitters, the first-base line; for left-handed hitters, the third-base line. If the bat crosses this 45-degree threshold, it is ruled a swing; anything less is considered a no-swing.

Each team is allowed to challenge one checked swing call per game. If the challenge is successful, the team retains the ability to challenge additional calls, allowing them to continue contesting checked swings as long as they are correct. After a challenge, the Hawk-Eye system’s determination—including a visual of the bat angle—is displayed on the ballpark video board, increasing transparency for players and fans alike.

The Official Baseball Rules do not define a checked swing, leaving the decision to the discretion of the home-plate umpire, who may consult with base umpires. This lack of clarity has led to frequent controversy and inconsistent calls. MLB’s new system aims to standardize the process, reduce disputes, and potentially lower strikeout rates by giving batters more leeway on borderline swings. The Florida State League has previously served as a testing ground for MLB’s experimental rules, including the Automated Ball-Strike (ABS) system.

“This is an early step in our testing process,” said Joe Martinez, MLB vice president of baseball operations. “At this stage, we are determining whether the technology works for this purpose and experimenting with different ways of weaving it into the game.”

This experiment is part of MLB’s broader efforts to integrate technology into officiating, with the possibility of wider adoption if the system proves effective at the minor league level.