Authorities across the country are investigating whether recent random and unsettling attacks on pedestrians are part of a game called "knockout" — in which teenagers try to knock unsuspecting passerby out cold with a single wallop.

Police say teens have made sport out of lobbing punches at strangers for years — and it's primarily a pastime for rowdy young boys trying to impress their friends.

But the moronic activity has taken a deadly turn — with at least two fatalities tied to "knockout" stunts this year amid evidence of a surge of similar assaults in New York, New Jersey, Pennsylvania, Massachusetts, Missouri, Illinois and Washington, D.C.

"It's hard to excuse this behavior, there's no purpose to this," Jeffrey Butts, a psychologist specializing in juvenile delinquency, told the AP. "When someone runs into a store and demands money, you can sort of understand why they're doing it, desperation, whatever. But just hitting someone for the sheer thrill of seeing if you can knock someone out is just childish."

In September, in Jersey City, two 13-year-olds and a 14-year-old were charged as juveniles in the slaying of Ralph Eric Santiago, 46. He was discovered Sept. 10 with his neck snapped and his head stuck between iron fence posts, according to the AP. County prosecutors have said they believe the accused teens were playing "knockout."

And in May, in Syracuse, N.Y., a pack of teens trying to knock out Michael Daniels, 51, with one powerful punch ended up beating and stomping him to death, according to the wire service.

A 16-year-old was found guilty of manslaughter, and his 13-year-old co-defendant pleaded guilty to assault — confessing he began the deadly beating by attempting to knock Daniels out cold with one blow. Both of the defendants were sentenced to 18 months behind bars.

Also in May, Elex Murphy, now 20, was sentenced to life in prison plus 25 years in St. Louis, Mo., for killing a Vietnamese immigrant as part the game in 2011.

In Lower Merion, Penn., a suburb of Philadelphia, two recent attacks may be related to the "knockout" game.

"We do worry that it's something like that ... because we've had two similar assaults, neither one of which resulted in a robbery," said Lt. Frank Higgins of the Lower Merion Township Police Department.

In one, two 19-year-olds were charged with knocking down a 63-year-old man out walking his dog the evening of Oct. 29. They were arrested nearby a short time later, and have been charged with assault, Higgins said. No arrests were made in the other incident from September.

Meanwhile in Washington, D.C., there have been two attacks in just the past week. One woman claimed she was surrounded by eight men on bicycles — one of whom punched her hard in the back of the head before riding away, according to NBC Washington.

Another victim, Phoebe Connolly, of Brattleboro, Vt., said she was randomly punched in the face by a teenager while riding her bike during a work-related visit to Washington last Friday. Connolly, who is 32 and works with teenagers in her job, said the blow knocked her head to the side and bloodied her nose.

"I don't know what the goal was," she said. "There wasn't any attempt to take anything from me."

A 78-year-old Brooklyn, N.Y., woman targeted by a group believed to be playing "knockout" became the ninth reporting victim of the game in New York — and some of the attacks are being treated as anti-Semitic hate crimes, according to NBC New York.

The New York Police Department has stationed additional officers in the Brooklyn neighborhood where nearly all of the attacks have occurred, mostly on Jewish people, according to the station.

Yet, while some of those attacked have been white, and some suspected attackers black, experts say the incidents are more about preying on the seemingly vulnerable than race or religion.

"It's about someone who is seemingly helpless, and choosing that person to target," Butts said.

"The behavior of the sudden assault of someone who seems helpless has appealed to the idiotic impulsive quality of adolescence forever," he added. "But there are now bragging rights beyond your immediate circle, when this is on television and online."

The Associated Press contributed to this report.