In December 1969, the Airplane played at the Altamont Free Concert at Altamont Speedway in California. Following the Grateful Dead's withdrawal from the program, they became the only band to perform at all three of the iconic rock festivals of the 1960s—Altamont, Monterey Pop, and Woodstock. Headlined by The Rolling Stones, the concert was marred by violence. Marty Balin was knocked out during a scuffle with Hells Angels members who had been hired to act as "security." The event became notorious for the fatal stabbing of black teenager Meredith Hunter in front of the stage by Hells Angels "guards" after he pulled out a revolver during the Stones' performance. This incident was the centerpiece of the documentary film "Gimme Shelter".