"I did a lot of stupid (stuff)," says Mark Zupan, this summer's unconventional action hero. "A lot of us did a lot of stupid (stuff). That's how we ended up like this."

"Like this" is in a wheelchair, a quadriplegic, never walking again. At 18, Zupan got dead drunk one night, crawled into the flatbed of a buddy's pickup to sleep it off, and was catapulted into a canal when the buddy, also drunk, ran off the road. He woke up when he hit the water and cried when his legs wouldn't move. His neck was broken.

"Like this" is also on the top-ranked U.S. quadriplegic rugby team, a maniacally ferocious athlete, barreling his souped-up wheelchair full speed into a competitor to send him sprawling to the floor and knocking the ball free.

Now 30, Zupan captains the team and stars in the new documentary "Murderball," which follows the players from the world championships in 2002 to the Paralympics in Athens, Greece, last summer.

Zupan and his teammates never listened when their mothers told them to stop or they'd break their necks. The crazy recklessness and boundary-trampling they had before their accidents make them driven champions, refusing to acknowledge any limitations of body or spirit.

They have groupies. They drink hard. They act like yahoos, insulting one another nonstop, playing outrageous pranks on the "ABs," the able-bodied. They relish the total violence of their sport and brag about their busted ribs and concussions.

"Where else can you hit somebody as hard as you possibly can or want to?" asks Zupan during a recent interview in Washington. "It sounds so sick and twisted and demented, but it's so much (expletive) fun." He grins.

Taut, intense, captivating and covered with tattoos, Zupan enjoys shocking and enlightening people "who think all quads are like Christopher Reeve." Technically, quadriplegia indicates impairment in three or four limbs, so there is a broad range of function.

Zupan's cervical injury left his legs immobile and his right arm weaker than his left, his right hand crooked. Asked whether he has sensation below the waist, Zupan says, "I can feel" — he pauses and smirks — "everything."

Not only can he have sex, the wheelchair can be good for picking up women, he says: "They always have a place to sit." And going through life at rear-end level, "the view's not bad."

"Of all the ways these guys challenged our preconceived notions, and made us confront what we thought about masculinity," says Henry-Alex Rubin, 31, one of the movie's co-directors, "the hardest was when we recognized they get hotter girlfriends than we do."

Zupan's blunt, profane acceptance of his life began only when he recognized he would never walk again. He put in two very bad years, angry and depressed.

When he flew out of the truck, he was just beginning independent life: a college freshman, away from home for the first time, playing Division I soccer at Florida Atlantic University. After surgery and rehabilitation, he came back to his parents' house. His dad had put in a ramp over the step and offered to bolt it down.

"I said, 'Don't bolt it down. That's gonna come up in no time. We'll kick this thing in six months.' And then it's six months, and you're going up the ramp, and I'm still in the chair, and it doesn't look like I'm going to be running any marathons," says Zupan. That was a bad time, when the bolts went in.

"You work hard and you do blood, sweat and tears" to recover as much as possible, he says. Then he hit the limitations of his new body. He told himself he wasn't a failure until he believed it. "This is out of my control," Zupan says. "And once you've come to terms with that, you can move on.

"It affords you opportunities to develop the relationships that you may have broken from when you were angry with the world."

Dana Adam Shapiro, the other director, grew curious about quad rugby after reading a 2002 newspaper article about it. Shapiro contacted his friend Rubin, who had directed "Who Is Henry Jaglom?" and worked on "Girl, Interrupted."

"He had me at 'quad rugby,' " says Rubin. The two filmed the world championships in Sweden and followed the team for the next 2 1/2 years, compiling more than 200 hours of film. "These guys had wills of steel," says Rubin. "They totally turned on its head every stereotype about guys in wheelchairs. They would mock our delicacy when we held the door for them. They are alpha quads."

"We deliberately filmed at waist level," says Shapiro, "so that we were showing everything from the point of view of the person in the wheelchair."

The two got an infusion of nearly a million dollars from ThinkFilm, and MTV is putting some marketing power into the movie. Zupan is starring in Reebok's "I Am What I Am" campaign. "He's supposed to be in his wheelchair, huge, on a billboard in Times Square," says Shapiro. "How wild is that?"

A civil engineer who works a 50-hour week, Zupan lives in Austin with his able-bodied girlfriend, Jennifer Wampler, and their boxer. He's in training for upcoming matches and ultimately the 2008 Paralympics. He lifts one to two hours, five days a week, and does five miles "in the chair," working on speed, endurance and agility. He also is increasingly making personal appearances before new quads, including Iraq war veterans.

"These guys are so damn young," he says, "just like I was. I've lived it, and I know how angry and defeated they can feel on any given day." He tells them about the 30 quad rugby clubs nationwide.

He tells them, if they ask, what he tells anybody.

Breaking his neck "was the best thing that ever happened to me. I have an Olympic medal. I've been to so many countries I would never have been, met so many people I would never have met. I've done more in the chair," says Zupan, "than a whole hell of a lot of people who aren't in chairs."