In the broad daylit afternoon of Tuesday, Sept. 10, a homeless man named Ralph Erick Santiago, 46, was walking along near downtown Hoboken, N.J., across the Hudson River from downtown Manhattan.

Three kids were following him, two 13-year-old boys, the other 14.

Unknown to Santiago, the three teens had taken the train from nearby Jersey City and were stalking him, determined to make him a victim in a violent and increasingly popular pastime among the nation's young — "knockout game" or "knockout king."

The game is simple, horrific and brutal. It's essentially a planned, deliberate attack: One or more kids strike a random target, regardless of age or gender, trying to knock them out with one punch. Often times, the attacks are videotaped for later enjoyment.

That day in September proved deadly. Without any warning, one or more of the teens punched Santiago in the back of the neck. The homeless man collapsed, and his head wedged itself between two posts in an iron fence. His neck was broken.

"I walk my dog a lot around here, and I see a lot of homeless," William Baily, who lived near the crime scene, told the Jersey Journal. "They get their sandwiches down the street. This is the first time I've heard of a crime like this happening here."

But it's happening a lot elsewhere. In places like St. Louis and Brooklyn and even London. And a lot of the attacks have been captured by security and cell phone cameras and are winding up online.

Ironically, Santiago was also attacked 27 years ago, which led eventually to his homelessness. He was a 19-year-old gymnast and break-dancer living in the Bronx in 1986. His wife at the time, Tracy Squillini, was eight months pregnant.

Santiago was beaten by an unknown assailant, his head pounded into the sidewalk, and spent a month in a coma. He was never the same again, experiencing physical and emotional damage that led to the couple's divorce, possible drug and alcohol abuse, and his eviction a year ago from his last known apartment.

Ten days after the attack this September, the three Jersey City teens were arrested and charged with his murder.

The game may have claimed their lives as well as Santiago's.