A security guard at the Cook County Juvenile Detention Center faces felony charges Friday.
Prosecutors say 27-year-old Michael Lynch body-slammed a boy when he refused an order to go back to his room.
That knocked the 15-year-old boy unconscious, and he was treated for a concussion.
Lynch's attorney says his client was breaking up a fight.
It was captured on surveillance video and witnessed by about ten other detainees.
Lynch was charged with aggravated battery and official misconduct. A judge set his bail at $25,000.