Checking in on MLB's tests of new check-swing technology

Juan Soto stood on the first-base line, took a breath and spit out a few sunflower seeds before heading back to the Mets' dugout in disappointment.

On the eighth pitch of a vintage Soto at-bat — which included hitting a potential game-tying three-run homer inches foul — he was questionably punched out on a check swing. It was the second out of the bottom of the ninth of an eventual 5-2 loss to the Reds on July 19.

“I didn't watch anything after the game,” Soto told Newsday the following day. “Definitely at the moment I just think it’s — I have like a 40/60 chance. So it was very close, but I felt like I didn't [go]. They make a decision, and it's just tough to the naked eye. It's whatever it is in the moment, the situation . . . I was frustrated because I grind that at-bat really hard, and then ended up like that.

“It's just disappointing for me.”

Whether or not you believe Soto actually went around, the only determination that counted was that of one man’s: third-base umpire Alex Tosi. But what if that check swing could be reviewed?

Throughout the history of baseball, check swings have been subjective. They are not defined in the official rulebook.

One day, that could change.

Major League Baseball is currently testing a check-swing challenge system in the Single-A Florida State League, home to both the St. Lucie Mets and the Yankees-affiliated Tampa Tarpons. It first debuted in the Arizona Fall League at Salt River Fields last year.

Using the same Hawk-Eye technology as the automated ball-strike challenge system (ABS), a swing will be called when the bat head moves ahead of the knob by more than 45 degrees.

Unlike the ABS challenge system, which was used in both spring training and the All-Star Game and ultimately seems like an inevitability in MLB, the check swing system is still in the very beginning stages of testing.

“I’ve never seen it before, so I can’t tell you if I like it or not,” Soto said. “But I don’t know. It’s just different.”

The system

The 45-degree number may not be deemed the right one, but MLB is trying to put a quantifiable measure on a call that has been strictly judgment-based.

For a lefthanded hitter, the angle matches the third-base line. For a righty, it matches the first-base line.

In the current FSL iteration, each team has one check-swing challenge at its disposal that it will retain until unsuccessful.

The FSL’s strikeout rate is slightly down since the test started on May 20. MLB has received positive feedback from both players and staff.

"We haven't made a decision about the check swing thing,” MLB commissioner Rob Manfred said at the June owners' meetings. “We do try to think sequentially about what's coming out. I think we've got to get over the hump in terms of either doing ABS or not doing it before you'd get into the complication of a separate kind of challenge involved in an at-bat . . .  We've really got to think that one through."

If both the ABS challenge system, which has been tested in the minor leagues since 2021, and the check-swing challenge system are implemented, a gray area could arise in situations with multiple challenges — one of a strike call and another of a check swing — happening on the same pitch.

But for the time being, it is something that has at least intrigued Manfred.

“I have to say, I'm fascinated by the technology,” Manfred said in an MLB Network Radio interview during the All-Star break. “It's unbelievable, actually. You can do too much on the field. I think the biggest thing that would really have to be thought through — you think about it — if you’re using ABS and the check swing, you could have two different challenges on the same pitch. That one gets a little complicated.”

Outfielder Drew Gilbert, the Mets’ No. 12 prospect per MLB.com, won the first check-swing challenge last Oct. 22, turning a 3-and-1 strike into a walk. He tapped his head to signal for a challenge, and the rest was history.

The Salt River Fields’ video board showed the Hawk-Eye animation, and Gilbert’s bat was clearly behind the 45-degree plane — a dotted line. His Scottsdale Scorpions teammates were awed.

“I thought it was unreal,” said third baseman Jacob Reimer, the Mets’ No. 6 prospect per MLB.com. “We heard about it before the game, just to test it out . . . if there was ever a call. So he went and tested it, and it showed up on the big screen like an aerial view of the bat and the ball. And it showed like a line, and his bat didn't cross it.”

When does a check swing become a full swing?

Last month, Mets lefthanded reliever Brooks Raley played three rehab games for St. Lucie ahead of his return from Tommy John surgery.

The 37-year-old Raley, who was drafted in 2009 and made his MLB debut in 2012, was introduced to the new system in short order.

“I had a guy challenge a check swing,” Raley said. “I actually won the call. But I don't really understand where they got the 45 degree. I think that's pretty aggressive. That's pretty much a full swing. Because if that ball is put in play, technically, that could go foul, pull-side foul. So I don't know.

“I don't really understand why it's 45 degrees. I'm more of a front of the plate and breaking the hands.”

Raley continued to break down his definition of when a check swing becomes a committed one.

“It's tough,” he said. “I think it's barrel. I think if the barrel crosses the plate, or past 90 [degrees], I think that's considered a committed swing. Obviously, we all know hitting is very difficult, but that's a pretty good commitment. I feel like if you could put the ball in play, if the ball were to hit your bat on its path, [it's] probably a swing.”

Soto’s plate discipline is among the best in the sport. He has a good relationship with umpires and an opinion that should be valued on the topic.

“For me, when you have total control of your barrel, I think you're never swinging until you probably break your hips in front of you,” Soto said. “I feel that's one of the main things.

“If you’re always under control with your barrel, you’re not swinging. Now, if you lose your barrel, that's when the swing comes in.”

Tweaks to be made

Jett Williams, the top prospect in the Mets organization, made one check-swing challenge while playing in the Arizona Fall League last year.

But it was not necessarily because he thought he would win it.

Williams, who has primarily played shortstop with Double-A Binghamton this year, had already seen his teammate Gilbert’s challenge victory. He figured he would give it a shot.

“I thought I definitely went, but the [technology] said I didn't,” Williams said. “But that's when I was kind of talking to some umpires of like, ‘Dang, we're really almost full swinging, and it's not a strike.’ I mean, it's awesome for us.

“But I was like, 'There's no way they're going to be able to use that in the big leagues.’ ”

With the current rules, one thing is clear: The designated 45-degree angle is significantly in the batter’s favor.

“They’re going to have to definitely tweak some stuff with it,” Williams said. “Just because I thought we were almost full swinging, and we were getting challenges correct.”

Said Raley: “I don't think 45 degrees [works]. I think that's pretty hitter-favored. I think it gets back more to, I don't know, 10 degrees or something. Something way, way closer to even.”

Home plate umpires will not disappear if or when ABS challenges — or, later down the road, check-swing challenges — come into play. Both Reimer and Williams noted the importance of maintaining the human element, but challenges — and the upside that come with them — can coexist.

“Over a course of a season, [check swing calls] can really impact a player's statistics,” Reimer said. “I know it's human element, but hitting’s already hard enough as it is. So calls like that can really help if we can get it to go our way more often.”

From pitch clocks to designated runners in extra innings, baseball has had plenty of change throughout Soto’s eight seasons.

He should see lots more of it in the next 14 years of his Mets contract.

“Anything that can help the game, I'm happy to see it and happy to hear about,” Soto said. “What the commissioner has been doing is just growing the game and doing good things. I think the MLBPA, too, is doing a great job to help us to increase the entertainment for the game and make it more extensive for the fans and even for players. So I think we're going on a good path.”

Newsday’s David Lennon contributed to this story.