Must admit I'd never heard of the 1949 Peekskill Riots in New York State. Now thanks to a tip from Bob from Brockley I am much wiser. The focus was an August concert featuring Paul Robeson, Pete Seeger, Woody Guthrie and other left-leaning singers, which was besieged by a cross-burning racist, anti-semitic, anti-communist mob. When the concert was rearranged on September 4th, the Ku Klux Klan and local cops seems to have co-operated to ensure that concert goers were ambushed in the woods on their way home. 150 people needed hospital treatment.
For the full story see this article by Jeffrey Salkin in the Jewish Daily Forward.