DENVER -- Boulder police issued tickets to participants after the 10th annual Naked Pumpkin Run turned rowdy Friday night and those found guilty will have to register as sex offenders.

The Boulder Daily Camera reported about a dozen people were ticketed after the naked runners started just before 11 p.m.

In the Halloween tradition, runners gather at a house to carve out pumpkins. Later in the night, they meet at a secret location (usually a nearby empty parking garage) shed their clothes and streak Peal Street wearing the pumpkins over their heads.

In past years, police mostly stood by as the crowd made its way up the popular pedestrian mall, but this year police managed to catch some before the run began.

"We wanted to do something before (the event) got out of hand," Police Chief Mark Beckner told the Camera. "This was a good opportunity to enforce the law."

Beckner said with Halloween falling on a Friday, more officers were on duty this year to hand out tickets. Streakers are like speeders, he said, adding you can't catch them all, but police do what they can.

“This isn’t OK,” he told the Camera. “It is against the law. You can’t do this with immunity.”

Veterans of the run told the Camera, surviving the race is all about letting go of inhibitions.

“This is my second time; it’s so liberating,” said Jill Fountain. “It’s a whole bunch of people taking off their clothes. It’s like making fun of being nude.”

The runners carry plastic bags carrying their clothes during the run. After the lap up, then down Pearl Street, they gather in front of the courthouse, dress and then disappear into the night.

And most important, the leaders warn, don’t throw away your pumpkin. This is Boulder, after all.