By Brad Segall

UPPER DARBY, Pa. (CBS) — Upper Darby police are looking for four teenagers who punched a man at a trolley stop and then posted the attack on a social media web site.

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Police say they have some pretty good evidence: surveillance from a nearby bank camera, the Facebook posting, and a still picture of the teen who threw the punch (top photo).

The incident happened last Thursday at the Aronimink trolley stop in Drexel Hill.  Police say the victim, who is homeless, was minding his own business when he was punched in the face.

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“It was a cowardly, mean-spirited, vicious act,” says Upper Darby police superintendent Michael Chitwood.  “There’s no other way to describe it.  There was no reason to do it other than this kid wanted to see if he could knock this guy out.”

Some call it “the knockout game,” and Chitwood says it’s the first time something like this has happened in Upper Darby.

Chitwood says his department began the investigation after members of the community saw the Facebook posting and called police because they were outraged.

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