1964 Philadelphia Riots:

At this point in time, racial tensions were so high that police tried to take extra steps to prevent rioting.  Now police patrols travelled in duos with one white cop and one black cop.  However, no matter what steps the police took, they could not prevent people from venting their frustration.  On August 18, 1964, a black woman was pulled over for a driving infraction.  She screamed at the two cops, and the two cops had to forcefully remove her from the vehicle in order to arrest her.  A nearby black man tried to help the arrestee by attacking the cops.  He was subdued and arrested as well.  Later that evening, rumors circulated that policemen had beaten a pregnant black woman to death.  Violence erupted and lasted two days.  No one was killed, but 341 people were injured, 774 people were arrested, and 225 stores were looted, damaged, or destroyed.