Spring position preview: DLs

We’re doing position-by-position previews in the weeks leading up to spring practice, breaking down the depth chart for one position group each day, paying special attention to things that can change in the spring.

We’ve looked at the quarterbacks, running backs, receivers, tight ends and offensive linemen so far. Today, we analyze the defensive linemen.

Lane Kiffin always said former USC defensive end Nick Perry was a unique athlete.

Everyone else finally saw the same thing at the NFL Combine in Indianapolis last weekend. Now the tough part comes, though: The Trojans have to replace him and the pass-rush presence he provided on the defensive line the last three seasons.

There isn't another returner on the line who has proven capable and consistent as a pass-rusher. Wes Horton has been effective in stretches and George Uko has shown flashes, but that's about it. Devon Kennard has struggled to get to the quarterback and the other projected starter, nose guard J.R. Tavai, doesn't even try to get there much.

Where will the sacks come from? That's part of what this spring will help figure out.

All things considered, the defensive line is probably USC's shakiest unit at this point, just over six months prior to the 2012 season opener. Only five returners -- the projected starters plus Kevin Greene, a reserve end -- have appeared in a game.

The three returners who will be key backups -- Antwaun Woods, Christian Heyward and Greg Townsend Jr. -- are all redshirt freshmen. Add in junior-college mid-year enrollee Morgan Breslin and high-school early enrollee Chad Wheeler, and that's everybody USC will have for the spring.

But it's the three redshirt freshmen who stand to benefit most this spring. Either Woods or Heyward absolutely must be a game-ready contributor for the Trojans this season, and the other has to at least be serviceable. Plus, with Greene's lack of development this far into his college career, Townsend Jr. could become the top backup at DE this spring if he shows he's picked up the mental side. (Top recruit Leonard Williams could shift a lot of that when he enrolls over the summer.)

Two other things to keep eyes out for: Is Breslin a potential player this year or does he need more seasoning, like USC's two junior-college offensive linemen, Jeremy Galten and David Garness, needed last year? And will the Trojans get Horton some practice time at defensive tackle this spring in case he's needed to take some snaps there during the season?

He's the only end with the bulk to make it viable.

Check back Wednesday for the linebackers.