The Los Angeles part of the movie, was filmed in Eagle Rock, Ca. You can google 1580 Colorado Blvd, that's the address of the street corner market, the video store is gone now but the doughnut store remains. The directors used local teens from nearby Franklin High school, to act in the movie. At the times gangs were prevalent in the neighborhood and they wanted to keep it authentic.
The role of Sgt. Freeborn was offered to Lance Henriksen.