Understanding the new Check Swing Challenge system MLB is testing in Arizona this fall

The first check-swing challenge in professional baseball history took place in the Arizona Fall League on Tuesday. New York Mets prospect Drew Gilbert, who plays for the AFL’s Scottsdale Scorpions, thought he couldn’t handle a 3-1 scoreline. The third base umpire called it a swing anyway, prompting Gilbert to tap his helmet and initiate a review.

In this first case it proved a success: the review ultimately concluded that Gilbert had not broken through the 45-degree plane.

“People like it, we’ll see,” Gilbert said. “I mean, obviously they need a little more trial and error. But it’s a good idea.”

Major League Baseball is testing a check-swing challenge system in the AFL this fall using cameras installed at Salt River Fields in Talking Stick, home of the Salt River Rafters. As the check-swing rule currently stands, if the manager or catcher believes that the home plate umpire’s ruling is incorrect, he will appeal to the first or third base umpire for advice to lodge an appeal. Whatever that referee says is final. However, there is another layer of verification under this new camera-based system. Catchers and managers still appeal to the first or third base umps, but if players disagree, they can now challenge and watch the video to see if the swing has crossed the 45-degree threshold , which distinguishes a check swing from a full swing.

The Scottsdale Scorpions and Salt River Rafters were informed before their game on Tuesday that a check would likely be called a swing, simply to try out the technology. Players would then have the opportunity to request challenges.

“I didn’t really know until about 10 minutes before the game,” Gilbert said.

During the Arizona Fall League, Mets prospect Drew Gilbert became the first player to challenge a check-swing call

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Only batters, pitchers and catchers are allowed to challenge a check swing, and each team has two challenges per game with an additional third if two challenges are made by the ninth inning.

Will this show up in the majors soon? No. The Check Swing Challenge system is currently nothing more than a proof of concept, said a person familiar with the development The athlete.

Rule changes that have undergone preliminary testing in the AFL in the past include the pitch clock, which has since been implemented in the majors, and the automated ball strike challenge (ABS) system, which has been implemented in all Triple-A -venues were installed in each of the last two seasons. Salt River Fields at Talking Stick is the only AFL stadium with the high-frame cameras critical to the Hawk-Eye system used for ABS and Statcast data in major league stadiums.

The MLB’s Official Baseball Rules do not provide a definition for a check swing, only that a strike is a pitch “hit by the batter.” The practical definition is when a batter swings just short of the first base line (for right-handed hitters) or the third base line (for left-handed hitters). This ambiguity raises some open questions as we begin these tests.

“I had a few questions, like I think the computer probably wouldn’t be able to detect these types of swings where a guy starts swinging and then almost gets hit by a pitch,” Scottsdale Scorpions manager Dennis Pelfrey said . “The run could go there, but if you have a feel for the game, most referees won’t call it a swing, but from a computer standpoint it certainly could be.”

Before MLB approved the pitch clock at the highest level, it was tested in more than 8,000 minor league games, the person with the knowledge said, to fill in gaps. A pitcher could step off the mound and a batter could call time to leave the batter’s box at any time, for example in the early stages of regulation. It is still too early to say when and if the check swing challenge will reach the minors.

But Pelfrey envisioned a perfect world in which the system would be available for baseball’s biggest games.

“The check swing, I think, is a really difficult call for the umpires because the bat comes in and out of the zone so quickly,” Pelfrey said. “I often feel like they’re guessing. But I think if we have these challenges in some of the game’s biggest moments — in the World Series in the ninth inning when someone gets stopped on a check swing — we can at least challenge it to see it.”

(Photo by Gilbert: Nick Cammett / Diamond Images via Getty Images)