Check Swing Challenge system comes to Florida State League

Major League Baseball will begin experimenting with using bat-tracking technology to call check swings starting tonight in the Single-A Florida State League.

The system, which was first tested in the Arizona Fall League last year, is designed to provide a definition of what constitutes an actual swing considering that none exists in The Official Baseball Rules beyond a pitch that “is struck at by the batter.” A swing or no-swing is left to the discretion of the home-plate umpire, who can ask for help from the first- or third-base umps.

Using the same Hawk-Eye system as ABS, a swing will be called when the head of the bat moves ahead of its knob by more than 45 degrees. Anything less than that will be considered a non-swing. For a clearer visual, the baselines both extend at 45-degree angles from home to first and third. Each club will have one Check Swing Challenge per game and will retain the challenge if it is successful.

The previous wiggle room has led to some wide interpretations of a swing over the years. Every so often, online clips (seen below) go viral from Game 7 of the 1965 World Series of Don Mincher nearly bringing the bat around his entire body on pitches from Sandy Koufax, only to be called as non-swings. Compare that to Game 5 of the 2021 NLDS that ended on a controversial swing call against Giants batter Wilmer Flores, who was ruled to have offered on a pitch low and away from then-Dodgers righty Max Scherzer.

As with many rules experiments that happen in the Minor Leagues, the Check Swing Challenge is not something that is imminently coming to the Majors. ABS, for instance, first came to the FSL in 2022 and has yet to find its way officially to The Show as it’s been continually fine-tuned, including the use of its own challenge system during this past Spring Training. The pie slice – two lines in the middle infield prohibiting the shift around second base – has been in place since 2022 with no further implementation elsewhere in the Minors or Majors.

But after decades of fans, players and coaches alike debating what is and isn’t a swing, MLB is willing to see what happens when it gives a more definitive answer in the Sunshine State.

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