Marcus Smith has seen just about everything as a member of the Arizona football team’s defensive line since coming on for former head coach John Mackovic’s final full season in 2002.

But one thing caught him by surprise against No. 3 USC Saturday, after lining up for his first career start at nose tackle in place of injured Yaniv Barnett.

“”Double teams,”” said Smith, a redshirt senior with 20 career starts at defensive end. “”That was the biggest difference.””

Smith had been a backup at end for Arizona since he was outshined by junior-college transfer Louis Holmes in the team’s season opener against Brigham Young on Sept. 2.

Smith said he was told by coaches the Monday before the Trojans game that he was going to start in lieu of Barnett, who has missed the last three games with a hyperextended elbow and an irregular heartbeat.

“”Whatever they need me to do, I’m going to do it,”” Smith said. “”I just want to play.””

The move seemed to pay dividends against USC, as Smith was able to use his long arms and quickness to fend off linemen Drew Radovich, Ryan Kalil and Chilo Rachal.

With Smith tying up the right side of the Trojans’ protection, Holmes got his third sack of the season – his first since getting two against the Cougars – and the Wildcat front four were able to help hold USC to its lowest point total since 2001.

“”Marcus has played a lot of football. He’s a big, strong guy,”” UA defensive coordinator Mark Stoops said. “”He can make the move fairly easy, and he’s come in and done a great job so far.””

More important in the short term for Arizona, the retooled unit – which is now also missing redshirt senior tackle Paul Philipp, who may not play another game for the team after suffering a severe knee injury Saturday – hasn’t skipped a beat on the field.

“”I think they’re really playing to our expectations. They’re playing really solid up front,”” Stoops said. “”The lack of depth with the injuries has slowed us down a bit, but I think overall we’re really pleased with the way they’ve played.””

With his knowledge of each position on the line, Smith has been able to help out Holmes, who lines up to his immediate left, with picking up the finer details of playing end during games.

Against USC, he reminded the newcomer of a pair of new calls the team has recently installed in its base defensive system.

“”If he has questions or anything like that, he knows he can come and talk to me if he needs any advice,”” Smith said. “”We’ve hung out a few times off the field, too, so we’ve got a pretty good relationship.””

Smith said he’s liked what he’s seen from Holmes, who has seemed to live up to the hype of being the nation’s No. 1 junior-college recruit this offseason.

“”He’s doing what he’s supposed to do,”” Smith said. “”It’s a big help to have somebody with his talent on our defensive line. Without him, I’d probably still be playing end, and who knows where we’d be inside.””

Barnett’s return, which the team isn’t going to rush given the nature of his heart condition, will return Smith to being an everyman, albeit the team’s best first option off the bench.

“”He’s the kind of guy that’s getting comfortable up front,”” Stoops said. “”He can play nose, he can play our three technique or D-end. He can play them all.””

Said UA head coach Mike Stoops: “”He’ll get better as he plays. That’s where we need him, inside.””