SEATTLE — Fabio Heuring was standing outside a Seattle nightclub on a Saturday night with a friend when a man bolting from a bouncer ran into them. The enraged man ripped off his shirt in the middle of the street and prepared to give Heuring’s buddy a beating.

Just then, in swooped a bizarre sight: a self-proclaimed superhero in a black mask and matching muscle-suit. He doused the aggressor with pepper spray, much to Heuring’s shocked relief.

A couple hours later, though, the superhero ended up in jail for investigation of assault after using those tactics on another group of clubgoers, sending pangs of anxiety through the small, mostly anonymous community of masked crime-fighters across the U.S.

Patrolling of city streets by “real life super-heroes” has been getting more popular in recent years, thanks largely to mainstream attention in movies like last year’s “Kick-Ass.” Many fret that even well-intentioned vigilantes risk hurting themselves, the public and the movement.

“The movement has grown majorly,” said Edward Stinson, a writer from Boca Raton, Fla., who advises real-life superheroes on a website devoted to the cause. “What I tell these guys is, ‘You’re no longer in the shadows. You’re in a new era. … Build trust. Set standards.’”

It’s not clear how many costumed vigilantes there are in the U.S. The website reallifesuperheroes.org lists 660 members around the world.

Benjamin Fodor, better known as Phoenix Jones, is part of a collection of vigilantes who appeared in Seattle over the past year. About two hours after he saved Heuring and his buddy, the 23-year-old man charged a group of people leaving a nightclub.

Fodor insists he was breaking up a fight when he hit the crowd with pepper spray; the people who got sprayed told police there had been no fight. He was briefly booked into jail for investigation of assault, but prosecutors haven’t charged him yet. He appeared in court last week while wearing his superhero costume under a button-down shirt.