Randomly knocking out unsuspecting strangers is a terrifying new 'game' being played by teenagers.
The resurgence of a dangerously violent street game that targets innocent bystanders has left people dead and others fearing for their lives.

The aim of the game, known as Knockout, is to approach an unsuspecting passerby and punch them so powerfully they are knocked unconscious. The attacks are violent, deliberate and in some cases, fatal.

Why? Simply "for the fun of it," said one teenage participant.

"They think it's funny," said another.

"They just go, boom, when it's the right time and the right place.

"It could be anybody, it could be a mother with her children. It's a macho thing."

The game first surfaced in New York City several years ago and after a short lull, a number of recent attacks are proving it's back, as violent as ever.

Reported incidents include a Washington, D.C. woman, who was walking home when she was punched in the back of the head by a group of teens on bicycles. They then sped away, laughing, reports WJLA.

Meanwhile in Denver, a 15-year-old was charged after he hit teacher James Addlespurger, 50, so hard he fell face first onto a concrete kerb.

"I was shocked at the whole narrative of it. There were six kids. There was me walking, just normally on my way, and boom came the punch and down I went, straight down with my face falling and hitting the cool concrete. I was shocked. I was speechless. I didn't really know what to think," Addlespurger told WTAE-TV.

In New Jersey, video footage shows Ralph Santiago, 46, targeted in broad daylight by a group of teens. He was later found dead with his head lodged between an iron fence, neck broken. Three teenagers, two 13-year-olds and a 14-year-old, were charged with his murder.

Other recorded attacks have taken place in New Jersey and Missouri, where a pedestrian was killed in each case.

"They just want to see if you've got enough strength to knock somebody out," said one participant.

Both the New York Police Department and London Metropolitan believe the attacks are evolving into predominantly race-based hate crimes.