Posted by ESPN.com's Ted Miller
That's a big hit for a USC offense that could have surrounded Sanchez with nine returning starters, with plenty of athletes available to replace graduating receiver Patrick Turner.
Sanchez's decision means that one of the most prestigious positions in college football is now again up for grabs.
Mustain, a high-profile transfer from Arkansas, was the 2005 Gatorade, USA Today and Parade Magazine national prep player of the year.
Corp was a Parade All-American in 2006. He's more mobile than Mustain. Mustain has a better arm.
During the regular season, the backup job alternated between them a number of times.
The wild card is incoming freshman Matt Barkley (Santa Ana, Calif./Mater Dei), who already has enrolled in school and will participate in spring practices.
Barkley is the No. 1 player on ESPNU 150, a list of the top 150 prospects in the country.
Barkley winning the job, however, would break the Trojans' pattern of valuing experience under Pete Carroll -- see Matt Leinart beating out John David Booty, Booty beating out Sanchez and Sanchez beating out Corp and Mustain.
Still, this will be one of the marquee competitions heading into the 2009 season, with none of the three candidates owning significant game experience that would distinguish him over the others.