Foo Fighters tease big event, but fans have no idea what it is

INGLEWOOD, CA - SEPTEMBER 21: Musician Dave Grohl of the Foo Fighters performs at the Forum on September 21, 2015 in Inglewood, California. (Photo by Kevin Winter/Getty Images)

Credit: Kevin Winter

Credit: Kevin Winter

INGLEWOOD, CA - SEPTEMBER 21: Musician Dave Grohl of the Foo Fighters performs at the Forum on September 21, 2015 in Inglewood, California. (Photo by Kevin Winter/Getty Images)