Quarterbacks look ahead

The competition for USC’s starting quarterback job in 2008 will not begin in earnest until the spring.

But with senior John David Booty being held out of practices to rest his still-healing finger during this off week, Mitch Mustain and Aaron Corp intend to seize the opportunity to share repetitions with backup Mark Sanchez.

Coach Pete Carroll said the competition, and what it foreshadows for the spring, is already palpable.

“When it shifts into this mode and we sit John David down you can feel it,” Carroll said. “It’s going to be really exciting to see.”

Mustain, the highly touted transfer from Arkansas, and Corp, a true freshman who starred at Orange Lutheran High, both performed well Tuesday in their first extended work with the first- and second-team offenses since the start of training camp.

Mustain, who started eight games as a freshman at Arkansas in 2006, has spent this season as the scout team quarterback, a job that enables him to work against the first-team defense but prevents him from mastering the nuances of the Trojans’ offense.

“I did OK for the most part,” Mustain said of his performance on Tuesday.

Corp has received limited reps behind Booty, Sanchez and Michael McDonald.

But he concluded Tuesday’s practice with two outstanding throws that moved Carroll to present Corp with a mock game ball.

“In the summer I didn’t know what the heck I was doing,” Corp said. “Now, I’m getting a little more comfortable in the offense. Not to say I have it perfect yet, but I definitely have progressed.”

While Sanchez got the chance to cut his teeth with three starts in place of Booty, Carroll acknowledged that Mustain and Corp are only just beginning to feel comfortable in applying what they have learned about USC’s offense.

Mustain and Corp are looking forward to December when the Trojans will have several weeks of bowl game preparation.

Carroll, like other coaches across the country, utilizes a portion of the practice time to evaluate players for the following season.

“That will be a good time to get a lot of good reps like we’re going to get this week, and I think we really need to use that because that will be the last chance we get before it’s real,” Mustain said.

Nose tackle Sedrick Ellis will be held out of practice this week to rest his right knee, which was drained of fluid Sunday.

“It’s no big deal,” Ellis said.

Ellis had arthroscopic surgery on the knee after last season’s first game.

He sat out three games and started the remaining nine.

Offensive tackle Sam Baker (hamstring) did a few drills before retreating to the training room for rehabilitation treatment, offensive line coach Pat Ruel said. . . . Tight end Fred Davis was absent because of flu symptoms, Carroll said.

The Trojans will practice again today with no pads. They will return to helmets and shoulder pads Thursday before taking Friday and Saturday off. . . .

Carroll was scheduled to introduce singer/songwriter Jeff Austin Black on Tuesday night at a showcase at Hotel Cafe. Black is the son of one of Carroll’s close friends.

gary.klein@latimes.com