The rules of the game are as simple as they are brutal. A group usually young men or even boys as young as 12, and teenage girls in some cases chooses a lead attacker, then seeks out a victim. Unlike typical gang violence or other street crime, the goal is not revenge, nor is it robbery. The victim is chosen at random, often a person unlikely to put up a fight. Many of the victims have been elderly. Most were alone.
The attacker charges at the victim and begins punching. If the victim goes down, the group usually scatters. If not, others join in, punching and kicking the person, often until he or she is unconscious or at least badly hurt. Sometimes the attacks are captured on cellphone video that is posted on websites.
"These individuals have absolutely no respect for human life," St. Louis Mayor Francis Slay said.
Slay knows firsthand. He was on his way home from a theater around 11:30 p.m. on Oct. 21 when he saw perhaps a dozen young people casually crossing a street. He looked to the curb and saw Quain sprawled on the pavement.
Slay told his driver to pull over. They found Quain unconscious, blood pouring from his head and mouth.
Quain was hospitalized for two days with a broken jaw, a cracked skull and nasal cavity injuries. He still has headaches and memory problems but was finally able to return to work earlier this month. Hundreds gathered in November for a fundraiser at the restaurant where he works, Joanie's Pizza, but he still doesn't know how he'll pay the medical bills.
"I don't remember much of what happened," Quain said. "I was hanging out with a friend, celebrating the Cardinals in the World Series. I went to the store and saw a group of kids who looked out of place, suspicious, but I shrugged it off. I got around to the library, and the next thing I remember is waking up on the corner with the mayor standing next to me. I tried to say 'hi' but my jaw was broken."
It isn't clear how long Knockout King has been around, nor is the exact number of attacks known. The FBI doesn't track it separately, but Slay said he has heard from several mayors about similar attacks and criminologists agree versions of the game are going on in many places.
St. Louis Police Chief Dan Isom said the city has had about 10 Knockout King attacks over the past 15 months.
Experts say it is a grab for attention.
"We know that juveniles don't think out consequences clearly," said Beth Huebner, an associate professor of criminology at the University of Missouri-St. Louis. "They see something on YouTube and say, 'I want to get that sort of attention, too.' They don't think about the person they're attacking maybe hitting their head."
Scott Decker, a criminologist at Arizona State, said the attacks are a modern extension of gang-like behavior instead of painting over another gang's graffiti as a show of toughness, they beat someone up and post a video on social media sites. The postings spur copycat crimes.
"It's adolescent and early adults, largely male, showing how tough they are. It's done to show off," Decker said.
Earlier this year in Chicago, a group of teens followed an elderly homeless man at a train station. One of the teens walked up to him and punched him in the face, knocking him out as the teen's friends laughed and mocked the man. The exchange was captured on video and posted on a hip-hop site, where it got about a quarter of a million views within two days. The teen was not arrested because police couldn't locate the homeless man to see if he wanted to press charges.
The crimes aren't limited to big cities. In 2009, Adam Taylor had just entered a parking garage in Columbia, Mo. Surveillance footage from the garage showed a group of teens following him. One of the teens attacked, punching Taylor and sending him crashing into a brick wall. A few seconds later, the others joined in, punching and kicking him as he lay on the ground. Taylor suffered bruising on the brain, whiplash and internal bleeding but survived.
Hoang Nguyen wasn't as fortunate.
The 72-year-old retired schoolteacher immigrated to St. Louis from Vietnam with his wife less than four years earlier to be near their daughter. The couple was returning to their apartment after walking to a grocery store on an April morning in broad daylight.
They took a shortcut through an alley, where they saw a group of young people approaching. Suddenly, one of them charged. Hoang was attacked as he stepped in front of his wife to protect her. The attack went on as he begged for mercy, she told police.
Hoang died of massive injuries. Elex Murphy, 18, was charged with first-degree murder and allegedly told police the attack was part of the Knockout King game. His attorney declined to comment.
St. Louis authorities are going to the source to combat further attacks. A special police squad has been assigned to focus on Knockout King, and a city prosecutor is designated for the attacks. But Isom said equally important is an outreach effort to talk to students.
"Certainly we take this very seriously and we're making every effort to stop it," Isom said.