The knee injury to quarterback Mark Sanchez at the start of Friday's practice raised questions about USC's depth at his counterpart position -- middle linebacker.
All-conference senior Rey Maualuga is the star of a strong linebacking corps but injuries to his backups, junior Luthur Brown and redshirt freshman Chris Galippo, have left the Trojans thin in the middle.
The last few days, true freshman Uona Kaveinga has gotten plenty of reps. As linebacker coach Ken Norton Jr. said: "Obviously the learning curve is accelerated."
Norton says he has been impressed by Kaveinga's size and intelligence, his ability to step in as leader of the defense. The assistant said things have changed since the mid-1980s when he was a freshman linebacker at UCLA.
"The high school programs are so accelerated nowadays," Norton said. "The [players] come up a lot more sophisticated."
Still, if Maualuga were unable to play, coaches might ask Brian Cushing to shift from his outside spot.
"He's actually more natural in the middle," Norton said. "We could put him in there."
The sight of Sanchez being carted off came as a shock to the receivers, the players who have perhaps the closest on-the-field connection to him.
For at least the next few days, they will be acclimating to new faces behind center with the first unit.
"All of them do something different," senior receiver Patrick Turner said.
Turner said that sophomore Mitch Mustain has experience and a strong arm, and redshirt freshman Aaron Corp has the mobility to be creative if the play breaks down.
"We've just got to bring them along and get them caught up to what we're doing on the first-team offense," Turner said.
Damian Williams played receiver with Mustain at Arkansas.
"We're still in the acclimatization period, so we're just trying to get used to the plays," he said. "Mitch is learning. Corp is learning. We've got to keep moving."
Coach Pete Carroll said the incident should remind all the backups on the team that they must be ready.
"I had the opportunity to say exactly that," Carroll said. "This is a classic opportunity for someone to step up . . . just like it is for some of the other guys at other spots."
Stepping it up
Friday was a good day for several USC players.
Sophomore receiver Travon Patterson made several impressive catches. Jurrell Casey played with the first-unit defense at nose tackle, a spot that remains a question mark.
Carroll compared the true freshman to former USC All-American Mike Patterson. He said they both have natural talent for the position -- and they both arrived on campus overweight. "He's already being monitored," Carroll said of Casey's weight.
The afternoon practice was not as inspiring for special teams. Twice, the snap on field-goal attempts ricocheted off an offensive lineman's leg and skittered across the turf.
USC is looking to replace Will Collins, who finished as a four-year starter at snapper.
Linebacker Kaluka Maiava missed the end of practice because of an injured shoulder. . . . Receiver Brice Butler was on crutches after suffering an ankle sprain during the morning walk-through.