Nov. 25, 2013 -- A 16-year-old girl in London was cold-clocked by stranger in broad daylight. In Manchester, England, a man died after being punched at a bus stop. A 78-year-old woman and a 12-year-old boy were both punched in the head in separate attacks in Brooklyn.
Some law enforcement officials believe these attacks are part of a disturbing trend known as "The Knockout Game," in which perpetrators pummel innocent, unsuspecting victims. Incidents have been reported in England and in several states in the United States.
There have been at least two deaths from similar attacks this year. Surveillance video of teenagers in New Jersey shows the group running away after punching a man who then had a seizure and died.
James Addelspurger, a 51-year-old English teacher at a creative arts high school in Pittsburgh and a popular local blues musician, was walking home one afternoon after work last year when he was attacked.
"I walked home through that alley for years, picked up a newspaper from the rack on the street, reading an article, put it through my arm, proceeded to walk through the alley, next thing I know, I was waking up answering questions to a police officer," he said.
Addelspurger said he has no memory of the incident, but the attack was captured on surveillance footage, which showed a passing 15-year-old boy punching Addelspurger, who fell hard and smashed his face on the concrete.
"That was a violent senseless act but I didn't know what happened until I saw the film," Addelspurger said. "I was in pain, I was confused, I was bloody."
Addelspurger said the incident made him angry.
"My initial anger from that, had no issues with anything, love teaching, teaching kids music, lover of life, lover of literature but when that occurred it was very senseless, very confusing, questioned humanity, the trust in people and so forth," he said. "But I do believe people are intrinsically good."
The worst part, he said, was seeing the 15-year-old and his friends on tape laughing at Addelspurger and then leaving him for dead.
For the first time, the young man who attacked Addelspurger talked about that day. He spoke to "Nightline" exclusively, but did not want his name identified or face shown. The now 16-year-old said the attack was "an impulse of stupidity, trying to show off for my friends."
"It was just like, 'let me knock this guy out, let me hit him,' basically like showing off to let them know I could fight," he said. "I feel guilty and embarrassed, ashamed."
The young man insists he had never heard of the knockout game when he attacked Addelspurger last year, but in recent days and weeks, there has been a spike of these kinds of attacks, which authorities believe may, in fact, be part of the game.
"Violence for us now is as American as apple pie," said Dr. Jeff Gardere, a psychologist and assistant professor at Touro Graduate School of Psychology in New York City. "We've become desensitized to it and there are some individuals who may not have a large menu of exposure to the arts to science to music all they're getting is the violence and they react to that."
In Washington, D.C., this month, Phoebe Connolly, who works with teenagers professionally, was punched in the face while riding her bike.
"Are they going to take somebody's money, are they going to take their cell phone? No, they're just going to knock you out? There's just no purpose for it whatsoever," she told ABC affiliate WJLA.
Last Friday in New York City, police charged one man for punching a 24-year-old Jewish man. Police said there have seven other similar attacks in Brooklyn and believe the motive may be related to anti-Semitism. All eight victims, including the 78-year-old woman, were Jewish and the NYPD's hate crimes task force is investigating.
"This I believe is a real economic issue where those who have nothing feel that they have nothing to lose," Gardere said. "Not only do they get a thrill out of doing something so horrific but then they get to watch it and then they get the positive reinforcement of people just watching these videos and these videos, no pun intended, getting hit after hit after hit after hit and these kids are finding some sort of immortality by their bad behavior."
But in the Addelspurger case in Pittsburgh, the 16-year-old perpetrator said race was not an issue.
"It was nothing," he said. "No matter who walked down that alleyway at that time they would have got hit, I'm just being blunt with you and giving it to you raw."
Some say the media may be exacerbating the problem by repeatedly showing these videos, but experts said parents can use this as a teachable moment, and talk to their kids about the dangers of not only being victims but also perpetrators.
The young man captured on surveillance tape from Pittsburgh was released a few months ago from a juvenile detention center where he spent nearly a year. He now said he is trying to turn his life around.
"I'm ashamed that I did that, embarrassed that I did that, wish I could take it back. I just felt like I owe him something," he said. "I'm going to feel like I always owe him something for the rest of my life."
As for other kids who might be tempted to randomly attack someone, the young man said they need to think twice.
"I wish I could take every kid who's doing that and put them what I've been through for a quick second and like they would just like, 'woah, I don't want no part of that,'" he said. "I guarantee they wouldn't even think about doing it. ... It's not even just the freedom and the juvie, the fact of knowing that you did that to somebody who didn't deserve it at all."