Members of the crowd watch The Black Keys, unseen, play at Lollapalooza in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Yo-Landi Vi$$er of Die Antwoord performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Tony Iommi of Black Sabbath performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Yo-Landi Vi$$er, left, and Ninja of Die Antwoord perform at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Michael Angelakos of the electro-pop band Passion Pit performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Ozzy Osborne of Black Sabbath performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Michael Angelakos of the electro-pop band Passion Pit performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Yo-Landi Vi$$er of Die Antwoord performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Ozzy Osborne of Black Sabbath performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Yo-Landi Vi$$er, left, and Ninja of Die Antwoord perform at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Ninja from Die Antwoord performs at Lollapalooza in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

DJ Vuilgeboost from Die Antwoord performs at Lollapalooza in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Ninja from Die Antwoord performs at Lollapalooza in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Ninja of Die Antwoord performs at the Lollapalooza music festival on opening day in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Ninja from Die Antwoord performs at Lollapalooza in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press

Yolandi Vi$$er, left, and Ninja from Die Antwoord perform at Lollapalooza in Chicago's Grant Park on Friday, Aug. 3, 2012.

Associated Press