May 18, 1907
William Mullen, a black strikebreaker for the Pioneer Truck Company, was delivering a shipment of lumber when he realized that he had lost some of his load and retraced his route to look for it.
At the Southern Pacific railroad crossing at Alameda and 2nd streets, Mullen noticed some lumber leaning against a shack belonging to a railroad flagman named Caulfield, who was presumably white. Mullen asked Caulfield if there was more of his lumber inside the shack and Caulfield said no.
Mullen challenged Caulfield, knocked him to the ground and began kicking him when Patrick Connelly, a union teamster for the Water Department and also presumably white, intervened, although it