Dangerous "knockout game" gaining popularity among youth

(CNN) -- It's frightening, it's deadly and it's gaining in popularity. It's called the knockout game, and it involves people going up to strangers, punching them and running away.

The dangerous game has police in several states on their heels.

The video above shows unsuspecting 50-year-old teacher, James Addlespurger, being violently attacked while walking near a group of boys.

The attack occurred in 2012 in Pittsburgh -- but the so-called "knockout" or "one hit quitter" game has apparently spread elsewhere.

In a few of the cases, the victims have died.