Mustain will be No. 2 this week

Mitch Mustain transferred to USC intent on becoming John David Booty’s successor as the Trojans’ starting quarterback.

Mustain, however, was fourth on the depth chart behind starter Mark Sanchez, Garrett Green and Aaron Corp for last week’s game against Oregon State.

So the low-key Mustain appeared more upbeat and confident than he has been in some time on Thursday after Coach Pete Carroll confirmed that he would back up Sanchez against No. 23 Oregon on Saturday.

“It was a big boost, “ Mustain said after practice.

Mustain, a third-year sophomore, ran the scout team last season after transferring from Arkansas, where he started and won eight games as a true freshman. He was expected to battle Sanchez for the starting job in spring practice, but Sanchez’s command of the offense was clearly superior and Mustain found himself competing for the back-up role.

A knee injury suffered by Sanchez in training camp put Mustain and Corp in a competition to possibly start, but Sanchez returned and Corp beat out Mustain for the No. 2 spot, holding it for the first two games.

Coaches, however, elevated Green from No. 4 to No. 2 for the Oregon State game. Now Mustain has leapfrogged two spots, portending a possible season-long game of musical chairs to keep the back-up quarterbacks motivated and competitive.

“Mitch has done better so he deserves a chance to be in that spot,” Carroll said.

The move allows Green to return to a pivotal role on special teams and puts Mustain in position to play if Sanchez were injured or ineffective.

“Hopefully I’ve made a statement this week, or at least up to this point, and I’ll continue that and solidify that into the next week or two,” Mustain said.

Cushing moves in

Linebacker Brian Cushing spent three seasons on the outside looking in as a strong-side linebacker. On Saturday, he’ll be the man in the middle, starting in place of injured senior Rey Maualuga at middle linebacker.

“He’s going to try and knock everybody’s head in just like he’s always done,” Carroll said. “He misses at times because he’s trying so hard to hit guys.”

Cushing, 6 feet, 3 and 255 pounds, was at his best this season against Ohio State. Though Maualuga stole the spotlight by returning an interception for a touchdown, Cushing played a more productive and disruptive role with 10 tackles.

Cushing began his career on the strong side backing up Dallas Sartz, played the “elephant” position along the line of scrimmage as a sophomore and now gets a turn in the middle. The versatility could help the prospects of a player already regarded as a first- or second-round NFL draft pick.

“Hopefully, they can see I’m not just an outside guy,” Cushing said of NFL scouts. “I can play inside too, and there’s more game film for the guys to look at.”

Third-year sophomore Michael Morgan will take Cushing’s spot at strong-side linebacker in his first start.

“I’ve been waiting for a long time but it’s finally here,” Morgan said. “I have to get out there and make the most of it.”

Quick kicks

Receiver Vidal Hazelton said he did not practice because of illness. . . . Receiver Brandon Carswell did not practice because of migraines, Carroll said. . . . Tight end Rhett Ellison is expected to be out three to four weeks because of a hairline fracture in his right fibula. . . . USC and the Los Angeles Sports Council Foundation are accepting donations for the annual “Touchdown for Youth” program, that will allow about 2,000 disadvantaged children to attend Saturday’s game. Each $30 tax-deductible donation goes toward a ticket and refreshments. Information: (213) 482-6333.

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gary.klein@latimes.com