Seth Lugo first heard the term “spin rate” in 2015, when he was buried in an organization teeming with pitchers who had thunderbolts for arms. To most, the righthander was a 34th-round draft pick with an unremarkable fastball, toiling away for the Mets’ Double-A affiliate in Binghamton, a 25-year-old afterthought.

Lugo never saw himself that way, of course, especially with a weapon that he had trusted since childhood. Now, he wanted to make it even better. That’s when Ian Levin, the Mets’ director of minor-league operations, pulled out a graph listing spin rates for every pitcher in the organization.

Lugo was ranked No. 1. Only one other pitcher was close. And it was all thanks to a nasty curveball, a gift bestowed upon him by his father, who had barely thrown the pitch himself.

One year later, Lugo was pushing the Mets into the postseason. Two years later, he is hoping to help stabilize a starting rotation that has faltered.

“I’m very proud of him,” Ben Lugo said. “That’s what he’s wanted to do his whole life.”

Spin rate is a secret no more, having become to curveballs what velocity is for fastballs. It is a measure that has come to form the core of Seth Lugo’s identity as a player.

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Consider the back of his baseball card. Topps No. 319 lists Lugo at 6-4, 225 pounds with a 5-2 mark and 2.67 ERA from last season. It notes how five of those wins came in his last seven starts, a big reason behind the Mets’ second-half surge toward a spot in the playoffs.

And then there’s this: “He threw one curveball at 3,498 revolutions per minute — the highest spin rate ever tracked by Statcast.”

“I think it’s kinda cool,” Lugo said. “I’ve always loved throwing my curveball, so I take pride in it.”

‘LIKE A KARATE CHOP’

The son of an Air Force man, Ben Lugo bounced around as a kid, never sticking around long enough to play organized baseball. Until adulthood, his experience in the game was confined to playing in sandlots. Even then, he never had enough arm to be much of a pitcher.

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Things were different for his son, Seth, who spent hours in the backyard throwing at a pitch return. Baseball brought the two closer, with the father attending clinics from more experienced coaches so he could coach his son’s teams.

It was at one of these clinics where Ben Lugo learned the curveball that would become a gift to his son. He was taught the basic grip, and how to throw it without straining the elbow. The ball had to come off the fingertips just right.

“You don’t twist your arm like turning a door knob,” Seth Lugo said. “It’s like you’re throwing a fastball but you turn your hand sideways, like a karate chop, straight down.”

The best training aid was an empty tennis ball tube. Seth was about 10 when he began spinning the tubes off his fingers, trying to throw them end over end lto repeat the proper motion. He got good at it.

One day, with Seth warming up on a bullpen mound, Ben got down into a crouch. He had never needed protective gear.

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This time, when the son unleashed his curveball, it dove sharply in front of the plate, hit the ground, and skipped between the father’s legs.

“And I’m like ‘wow,’ ” Ben, 55, said, laughing at the first sign that Seth might be onto something special. “I said from now on, you’ve got to have a catcher back there. I don’t catch you anymore.”

The curveball became the great equalizer. Other kids might have thrown harder. But none of them could spin a baseball like Seth Lugo.

“When I threw it, no one could hit it,” he said. “So I fell in love with it.”

Once, while playing travel ball, Lugo fired a curveball that fooled a batter so badly that he ducked out of the way, thinking it was at his head. Then the ball broke back over the plate, where the batter had moved his head.

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“I thought it was going to be a strike,” he said. “But I broke his nose.”

‘TRYING TO OVERDO IT’

Years later, Lugo’s surprise introduction to his spin rate data only reinforced what years of awkward reactions had taught him about his curveball. But the information led him to a strange place, at least at first. He found himself trying harder to make the pitch even more unhittable.

For awhile, it was almost counterproductive.

“For me personally, I think that kind of information might have gotten into my head a little bit, trying to overthrow it, and I think it kind of got my release point out of line,” Lugo said. “I think that caused me struggling for a couple of years, trying to overdo it now that I see numbers to it.”

Eventually, Lugo got over the mental block. He resisted the urge to pitch to his spin rate, and reminded himself there was more to pitching than spinning curveballs.

“Just like a hitter with a lot of power isn’t necessarily a power hitter,” Levin said. “You still have to be able to use it in a game. So spin rate in this case shows that he has the ability to spin the ball exceptionally well, which means it’s going to move a greater amount. But you still have to be able to command the pitch and use it effectively.”

Back in 2015, when Lugo first saw the spin rate chart, he naturally gravitated to the name closest to his. Former Mets farmhand Dawrin Frias also had shown the uncanny ability to spin curveballs.

But unlike Lugo, Frias lacked command of his arsenal. Later that summer, Frias was sent to the A’s as the player to be named in a trade for Eric O’Flaherty. A year later, Frias was out of organized baseball, while Lugo was breaking into the big leagues.

Not long after his debut, an encounter with the Marlins’ Dee Gordon let Lugo know that he could still baffle hitters with a curveball that has remained virtually unchanged since childhood.

“I’ve re-watched the video a few times,” Lugo said. “The first time I faced Dee Gordon, I got him two strikes and I threw one. I think he yelled a cuss word. He fouled it out off and yelled a cuss word back out of the box. He looked at me and pointed or something. It was pretty funny.”

‘LIKE NORMAL’

Arm injuries come for pitchers, no matter what. The time came for Lugo late in spring training, shortly after his return from the World Baseball Classic. Doctors found a partially torn ligament in his elbow. Fluid found in the area led the Mets to believe that the injury was suffered sometime recently, perhaps during the tournament.

Opening Day arrived with Lugo on the disabled list. Weeks of rehab awaited. But as he progressed to his minor-league rehab, and the time had come to start spinning curveballs, he had to know. Would it be the same?

“It’s the same thing with velocity,” Lugo said. “You do it with a fastball. So why not check it out with a curveball?”

What he saw on the chart reinforced how he had felt on the mound, that he could still throw the pitch “like normal.” At little more than 3,400 RPMs, the curveball he learned from his father had remained intact.

“With all the hype from last year, I was just curious about it,” Lugo said. “I don’t know anything about my elbow. I was just curious about if the curveball would be the same. And it was.”