NEW YORK – Cletus Seldin, with his head wrapped in an American flag bandana, wearing a full beard and a hooded sweatshirt, would have looked as at home underneath a truck fixing a transmission as he did moving about the ring at Mendez Boxing Gym for Wednesday’s media workout.

His blue-collar appeal has served him well in his career, making the unbeaten junior welterweight from Shirley, Long Island, one of the Metropolitan area’s top ticket sellers. This Saturday, Seldin makes his HBO debut at Nassau Coliseum against Roberto Ortiz in a 10-round bout that opens up the broadcast.

The card features Brooklynites Danny Jacobs and Jarrell “Big Baby” Miller against Luis Arias and Mariusz Wach, respectively. As Seldin sees it, he’ll be feeling the support as the only true Long Islander on the televised card.

“The majority of the fans are my fans,” said Seldin (20-0, 16 knockouts), known as “The Hebrew Hammer.” He calls his fans “Hammer Heads,” and expects a few hundred of them to be in the arena screaming their heads off — and tailgating like they’re at a Jets game outside of it. Their reputation precedes them, and their presence will be unmistakable to anyone in the building.

“As soon as you get to the venue you’ll go ‘that’s a Hammer Head, that’s a Hammer Head.’ They are loud, obnoxious, a little buzzed, but they’re my family and my friends, so you gotta respect them,” said Seldin.

Seldin is a mild-mannered guy for the most part. That is, as long as you don’t mess with his Funko Pop “vinyls.” And definitely don’t call them dolls.

“I have one of the largest collections in the country. I even wear a glow-in-the-dark Chase patch on my trunks,” says Seldin. He says he got really into collecting the figures when his girlfriend bought him one, and soon they found themselves going “Pop hunting” at events like New York Comic Con to expand his collection, which he estimates to be worth about $60,000, with his most expensive one being about $3,000.

“I think there’s two people in the world that completed the Star Wars line and I have a ridiculous amount of Star Wars Funko Pops. I have about 500 in just Star Wars,” said Seldin.

“It’s a really big addiction, but I love it because it keeps me away from boxing. Nobody who collects them knows anything about boxing, so they treat me like a regular person, so that’s awesome,” he adds. He isn’t too hot on anyone so much as looking at his collection, and warned future opponents, and anyone in general, about ringing that bell when it comes to his hobby.

“If you mess with my Pops, you’re dead. It’s that simple.”

Though named after ‘50s Yankees infielder Clete Boyer, Seldin doesn’t swing a bat. But he has shown he can hit pretty hard with his overhand right. He’s been matched cautiously in his career and saw it stall at one point, due in part to when his fight against Mike Arnaoutis was canceled this past June after Seldin tested positive for elevated testosterone levels in a random test by the Voluntary Anti-Doping Agency, which conducts testing for WBC’s Clean Boxing Program.

He returned to the ring in late September after 15 months out, banging away a decision against Renald Garrido.

Ortiz (35-1-2, 26 KOs) has also had false starts in his career, like when his fight against Antonio Orozco — set to open HBO’s September 23 broadcast featuring Jorge Linares facing Luke Campbell — was canceled after Orozco weighed in seven pounds over the limit. Ortiz, who like Seldin is 31, is 4-0-1 since his lone defeat, a second-round knockout to Lucas Matthysse on a left hook to the body, after which Ortiz barely missed the count.

Seldin describes Ortiz as a “tough Mexican” whose style will mesh with his for an exciting brawl, the kind of fight that’ll further get his foot in the door opened by HBO.

“His style and my style is why HBO brought us, because they’re gonna see one action-packed fight,” said Seldin.

Seldin’s promoter, Joe DeGuardia, sees this fight as a way for Seldin to make up for lost time and then some if he can pull off the win.

“A win over Ortiz on HBO will be a huge springboard for him, and we’d be looking for a world title fight or high-profile match against a big name next,” said DeGuardia.

If Seldin can be half as combative in the ring as he is when someone messes with his Funko Pops, he should be a handful to deal with on fight night.