There is a frightening new trend in locker rooms, backyards and basements across the country: unsupervised children and teenagers pummeling one another, wearing only athletic helmets and gloves for protection.
It's a risky new twist on "Fight Club," where anything goes.
"There are no rules, that's the rule," said one teenage boy.
Hundreds of these fights have turned up on the Internet, on sites like YouTube.com, which shows kids locked in hand-to-hand combat.
Some of the videos show boys battling until someone loses a helmet or gets knocked out.
No-holds-barred fighting has long been popular on television, in shows like "American Gladiators" and "The Ultimate Fighting Championship."
But medical and sports experts have grave concerns that backyard helmet boxing could result in serious, lifelong injuries.
"These are children who are getting concussions out of what they think is a sport," said Fred Mueller, an exercise and sports science professor at the University of North Carolina.
Scott Randles was a hockey star at his high school before he took his obsession with helmet boxing too far.
"Looking back, it is the stupidest thing I ever did, because it changed everything," Randles said. "Sometimes I blank out, and I go look at the clock and it'll be two minutes later or something, and it's a lot harder to learn stuff and it's a lot harder to remember things."
With its popularity on the rise, doctors and parents say the best way to end this troubling trend is to educate the public about its dangerous consequences.
"It's not a game," said Sharon Randles, Scott's mother. "I know other parents don't know about this, and it's happening all the time and this has to stop."