That's a good starting point. St. Patrick's Day, 1979: An all ages show at the Elks Club in Los Angeles degenerates into a police riot. The cops just invaded and beat the hell out of everyone. There are photos on a few of the linked sites of various injured punks.
As others have said, that was the end of innocence. It was war between the LAPD and punks after that.
This all happened when I was just finishing junior high school in Orange County, so I didn't have the opportunity to be attacked by the LAPD until my freshman year of college when I was in a crowd at the Street Scene and they charged us with horses, medieval style.