Some of the people wondering were USC fans. Others were Division I college football coaches looking for an experienced quarterback with a winning pedigree.
Mustain estimates he got 10 phone calls from other programs after NCAA sanctions were announced two months ago. Everyone knew the senior was blocked by sophomore quarterback Matt Barkley and probably would play his entire USC career as a backup, so some coaches used the cover of the Trojans' bowl ban to do a little late-career recruiting.
"I wasn't upset or anything," Mustain said. "I just wasn't interested."
It might seem odd that Mustain would accept a reserve role at USC when starting jobs were there for the taking, but his decision to stay was a calculated one. Mustain has hopes of playing in the NFL and USC runs a pro-style offense. He figures the experience on USC's practice field is more valuable than the chance to play on Saturdays somewhere else.
He has an example.
Matt Cassel never started a game at USC, stuck behind Heisman Trophy winners Carson Palmer and Matt Leinart, but the New England Patriots picked him in the seventh round of the 2005 draft anyway. Cassel rode the bench three more seasons in New England, then jumped when an opportunity finally arrived. He took over after Tom Brady's knee injury in 2008, had a great season and parlayed that into a six-year deal with the Kansas City Chiefs worth more than $10 million a year.
Can it happen twice, a quarterback graduating from the USC practice field straight to Sundays? It might be a long shot, but don't write it off. NFLDraftScout.com has Mustain rated the No. 11 quarterback in next spring's draft and estimates he'll be taken -- you guessed it -- in the seventh round.
Mustain was smart enough to size up the opportunities. He had played in a run-oriented, spread offense at Arkansas, winning his first eight games as a freshman starter before transferring to USC in 2007. He knew most college systems wouldn't display his talents to talent evaluators at the next level.
"I decided to stay that extra year and I think that was a big part of it, knowing guys can make the transition from here," Mustain said. "You see guys throw for 20,000 yards in their career that can't make the transition."
Leading an NFL-style offense has become such a technical job that quarterbacks who ran spread offenses in college, like the Denver Broncos' Tim Tebow, often need years of study to get up to speed. Mustain has been doing his studying on campus, and the coaches say he finally has a firm enough grasp to run the offense smoothly. Like any other job-seeking college graduate, Mustain wants to be prepared for the next phase of life.
"You've got to be able to get on the board in front of GMs and coaches come January, February and March and explain what you're doing, explain protections, that you understand where the O-line is going, that you can command an offense," Mustain said. "I feel like this is the best place to learn that."
Mustain's improvement benefits USC, too. In a season defined by a lack of depth, quarterback is one position where the Trojans look well-protected. Should Barkley get hurt, Mustain can run the offense for a game or more, perhaps without it missing a beat. He outplayed Barkley at times during the spring, even though Mustain didn't throw a pass in a game last season. In 2008, he was 11-for-16 for 157 yards and two touchdowns.
"That's very exciting to have a second guy that you feel you can call anything with," coach Lane Kiffin said. "That's unusual, so we feel like we're in a good spot there."
It's also good Barkley knows Mustain is there. The only other experienced quarterback, Aaron Corp, transferred to Richmond. Mustain and Barkley are the leaders in offensive meetings and they push each other in practice, often splitting the reps this early in camp. The last thing USC coaches want Barkley to be, at 19 years old, is complacent.
"It's not that fun when you're kind of like the alpha dog and there's no competition," Barkley said. "Then you have to obviously compete against yourself, but it's easier to challenge yourself when you have a guy like Mitch, who's right at your tail and making plays and challenging you to be a better quarterback."
Mustain, once ranked as one of the top high school player in the country, is unlikely to have a decorated college career to look back on, but he'll leave college with what he's supposed to leave with: an education in his chosen field.
"That didn't change when [Pete] Carroll left. That didn't change with the sanctions," Mustain said. "I'm going to finish out my last year and see what happens."
Mark Saxon covers USC football for ESPNLosAngeles.com.