Inspired by the 1999 film Fight Club, starring Brad Pitt and Ed Norton, underground bare-knuckle brawling clubs have sprung up across the country as a way for desk jockeys and disgruntled youths to vent their frustrations and prove themselves.

"This is as close as you can get to a real fight, even though I've never been in one," the soft-spoken Siou said.

Despite his reserved demeanour, he daydreams about inflicting pain on an attacker. "I have fantasies about it," he said.

In recent months, police in New Jersey and Pennsylvania have broken up fight clubs involving teens and preteens who posted videos of their bloody battles on-line.

Earlier this month in Arlington, Texas, a high school student who didn't want to participate was beaten so badly that he suffered a brain hemorrhage and broken vertebrae. Six teenagers were arrested after DVDs of the fight appeared for sale on-line.

Adult groups are more likely to fly under the radar of authorities.

Menlo Park police hadn't heard about the local club and said they wouldn't be likely to take action because the fights are on private property between consenting adults. That could change if someone complains or is sent to a hospital, police said.