In this undated image provided by the University of Southern California, USC quarterback Matt Barkley throws during football practice in Los Angeles. Sophomore Aaron Corp has emerged as USC's No. 1 quarterback at the end of spring practice. Freshman Matt Barkley will be his backup and junior Mitch Mustain is slotted as the No. 3 QB, although coach Pete Carroll says the competition to replace Mark Sanchez will continue into fall camp.(AP Photo/University of Southern California)