Amateur video of an older man being knocked out by a young subway rider has caught national attention and prompted a police search for both the attacker and his victim.

In the video, an elderly man wanders through a crowd of young men (possibly teenagers) congregated on the Red Line subway platform in Chicago, Ill. One of the young men follows the older man, they exchange a few inaudible words, and the young man punches the old man square in the face, knocking him flat on his back. The hit was so hard that the man's hat fell off on his way down.

The group immediately boards a waiting train, laughing and joking about the incident, while a woman attends to the victim.

The video appears to have been taken by someone in the group of young men accompanying the attacker, as it follows them from the platform onto the subway car. It was initially uploaded to, where numerous amateur videos of subway incidents in multiple U.S. cities can be found.

According to the Chicago Tribune, the incident took place and April, and the injured man was treated and released at Northwestern Memorial in Chicago. The Tribune also reports that the young man has been named on some Web sites, but has not been charged.

The police are reportedly also seeking the victim to determine if he wants to press charges.

Warning: This video contains disturbing content.