That was the Rolling Stones At Altamont.
("Altamont, December 6, 1969, was supposed to mark a glorious end to the Rolling Stones’ US tour. Instead, Hells Angels ran riot.")
the Grateful Dead asked the hell’s angles to provide security at one of their concerts.
If you are thinking about Altamont December 1969...it was the Rolling Stones that had the Hell’s Angels as security. The Grateful Dead did not even play although they were scheduled. Once they heard that Marty Balin of Jefferson Airplane had been beat by some Angels, they pulled out. The Dead recorded a song about the whole ordeal titled “New Speedway Boogie.” Just thought I would correct the record. One of the earliest known versions of the song was played December 20th 1969 at the Fillmore in SF.