A longtime Mets fan gave new meaning to the words “die-hard” after he was blasted in the face with a T-shirt cannon in Citi Field, knocking him unconscious and nearly blinding him, according to a new lawsuit.

Alex Swanson, 54, says the 100% cotton missile smacked him square in the eye, knocking him off his feet and leaving his retina dangling by a thread at a Mets shutout against San Francisco over the summer, according to the suit filed Friday in Queens Supreme Court.

“It could have killed me,” he said. “It’s a hazard.”

It was a near perfect day on June 5 when he got to the stadium with his four sons, outfitted head to toe in fan gear.

The Smithtown, L.I., father of three said he and his boys were so conspicuous that a reporter with SportsNet New York interviewed them on their way into the stadium.

Everything seemed to be going their way. The Miracle Mets were up 6-0 at the seventh inning stretch as the T-shirt shooters made their way to where the Swansons were sitting on the Pepsi Porch.

Swanson walked down to the rail, hoping to add another shirt to his collection when the guy operating the T-shirt cannon seemed to be having trouble with his shooter.

The man lowered the muzzle to deal with the issue — and discharged the tightly wrapped jersey into Swanson’s face from 20 feet away.

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Dougherty/Getty Images) NEW YORK - SEPTEMBER 28: Former New York Mets players Rusty Staub waves to the fans at home plate after the game against the Florida Marlins to commemorate the last regular season baseball game ever played in Shea Stadium on September 28, 2008 in the Flushing neighborhood of the Queens borough of New York City. The Mets plan to start next season at their new stadium Citi Field after playing in Shea for over 44 years. (Photo by: Al Bello/Getty Images) NEW YORK, NY - OCTOBER 11: Board member Daniel J. 'Rusty' Staub speaks during the 27th Annual Gala Of The New York Police And Fire Widows' And Children's Benefit at Park Avenue Armory on October 11, 2012 in New York City. (Photo by J. Countess/Getty Images) NEW YORK, NY - APRIL 01: Former New York Mets player Rusty Staub throws out the first pitch to Catcher Anthony Recker #20 of the New York Mets before the game against the San Diego Padres on Opening Day at Citi Field on April 1, 2013 in New York City. 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The doting dad said he was knocked off his feet and fell backwards, hitting his head and blacking out.

“The guy who shot the gun scampered away,” Swanson said.

When he came to, he was surrounded by his sons and Mets support staff. He was taken to the nurses station, but refused to go to the hospital because he could still see, despite his eye being badly swollen.

A CAT scan the next day found he’s suffered a concussion and severe eye trauma that he still deals with to this day, said his lawyer Dustin Levine of Ancona & Levine in Mineola. His retina was nearly completely severed, left hanging by a thread, the suit claims.

“I still have floaters — little black specks — over my cornea,” Swanson said. “The doctor says the retina could detach at any moment.”

“It’s like someone is shining a flashlight in the corner of my eye," he added.

He said the Mets back office reached out to him and offered him free tickets, but that’s not good enough for Swanson.

“First and foremost they should stop using that gun,” he said. “It bothers me because it could have hit a little kid. I don’t know why they use them anymore.”

The Mets did not respond to multiple messages left for comment.

A 2016 study of the dangers T-shirt cannons conducted by West Point Military Academy found they do indeed have the power to injure.

“The folded T-shirts achieved kinetic energies fifteen times larger than that of a paintball gun, nine times larger than that of a pellet gun and nearly half that of a 9mm handgun,” according to the authors.

This past April, a woman sued the Houston Astros for $1 million after she claims her hand was injured by a T-shirt cannon.

The Texas team is fighting the suit.

Through it all, Swanson’s devotion to the Mets’ star players is unwavering.

“It’s not Todd Zeile’s fault or Todd Frazier, it’s the people who run the Mets,” he said.

His lawyer hasn’t put a price on Swanson’s injuries.

“I just want there to be accountability and just compensation for my client,” Levine said.

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