See also: Destinations for Outdoor Lovers
The video, which appears to have been shot in April, was posted on the website World Star Hip Hop last weekend and immediately went viral.
It shows a teen walking up to a man who appears to be homeless and punching him, as his friends laughed.
A Facebook page identified a man they say is the attacker in the video and urged that he be brought to justice.
Fox Chicago spoke to a woman the TV station reported was the attacker’s mother. She reportedly admitted her son was the attacker, and said he had been “going through some things.”
The Chicago Transit Authority told Fox Chicago they were looking into the matter. They did not immediately respond to a request from the News for comment.