The defensive line rotation

USC already has its starting defensive ends identified in Devon Kennard and Wes Horton, and its top three tackles organized too.

But that's not enough. The Trojans need more linemen capable of logging 10-20 snaps a game to provide breathers for the starters. Who will back those five guys up against the fast-paced offenses of the Pac-12?

"That's the big question," USC defensive line coach Ed Orgeron said last week.

Orgeron has dedicated this spring to cultivating some playable backups for the 2012 season. And as of right now, he says, he has four potential players: redshirt freshman Greg Townsend Jr., junior Morgan Breslin, redshirt junior Kevin Greene and incoming freshman Leonard Williams.

Realistically, those four are competing -- or will be competing, in Williams' case -- for two slots behind Kennard and Horton.

"There's gonna be a third and a fourth end," Orgeron said on Saturday after the Trojans' scrimmage at the Coliseum. "But there is a big difference between the first team and the second team right now.

"Those guys have to rise and I have to do a better job of coaching them to get ready."

At defensive tackle, redshirt sophomore George Uko will start at the three-technique and it's starting to look like Antwaun Woods will start at nose tackle. But Woods and fellow second-year man J.R. Tavai will split the snaps there, in some form.

Redshirt freshmen Cody Temple and Christian Heyward are the options for the needed fourth tackle, but both are out for the rest of the spring. Temple underwent surgery last week on his ankle and is expected back for fall camp; Heyward is still recovering from offseason shoulder surgery.

"Really, a guy that was showing promise was Cody Temple," Orgeron said. "That would be our fourth guy right now."

Orgeron has been most pleased with Kennard and Horton, the two seniors who shared time with now-NFL hopeful Nick Perry on the corners last season. He said the two have emerged from the shadow Perry's athleticism and NFL potential created on the defensive line.

"Nick was the guy last year and I think they were kind of overshadowed a little bit," Orgeron said. "I don't think they liked it, and I don't blame them one bit.

"Nick was a really good player for us, but these guys bring some different things. They're not probably as gifted as Nick, but they're really good in some other areas."