Before every USC football season, the athletic department plasters action photographs of the team’s premier players on a poster that advertises the season schedule.

Choosing the faces of the Trojans’ defense was presumably a bit thornier this season than in years past. Junior safety T.J. McDonald was a no-brainer considering in 2010 he led the team in tackles and notched three interceptions in the process of becoming an All-Pac-10 second team honoree. Choosing a second player to pair with him proved more difficult, however, but the department settled on senior defensive tackle Christian Tupou, who, despite being a three-year starter entering the season, sat out all of last year after tearing ligaments in his left knee in the 2010 spring game.

Baby steps · Junior safety T.J. McDonald is part of a secondary that allows opposing quarterbacks to throw for 10 more yards per game compared with last year. The rush defense, however, is allowing opposing tailbacks to run for 41 fewer rushing yards per game. - Carlo Acenas | Daily Trojan

Though many players flashed with potential entering 2011, many needed to convert promise into consistent production. So far in 2011, the defensive results have been mixed.

“We had a good week of practice before Cal, and we hit two pretty good teams in Arizona and Arizona State and we didn’t play very well,” USC assistant coach Monte Kiffin said. “That combination obviously wasn’t very good. But we’ve challenged ourselves, and we’re gaining more confidence.”

Despite Kiffin’s optimism, the statistics do not indicate substantial improvement over last year’s defense that ranked 84th in overall defense and 109th in passing defense, surrendering nearly 260 passing yards per game and a 59.9 opposing quarterback completion percentage. This season’s pass defense is statistically worse, as USC’s opponents have averaged 271.7 passing yards per game with a 64.7 completion percentage. To USC’s credit, the defense is allowing 41 fewer rushing yards per game in 2011 (140.5 yards per game in 2010 compared to 99.5 yards per game in 2011).

What is most troubling about these statistics is they do not yet include three of the most potent offenses USC will face this season: Notre Dame, Stanford and Oregon. The Fighting Irish possess one of the most balanced attacks in the nation, ranking 29th in passing yards and 29th in rushing yards in the FBS and scoring 32.3 points per game.

“Notre Dame’s offense is really good,” Kiffin said. “You can’t be more balanced than they are. Last year they were more of a passing team, but they’ve developed a pretty good running team this year.”

Though the defensive numbers appear grizzly, there are certain developments that indicate USC might be due for a defensive resurgence. Certain USC players at critical positions who have battled bouts of inconsistency are beginning to show upticks in their play.

Redshirt junior defensive end Wes Horton, who registered only his second sack of the season in the waning minutes of the game against Cal, indicated pass rushing is predicated on confidence — something he might have regained against Cal.

“There were two or three games where I had a stretch with no sacks and confidence is huge when it comes to being a pass rusher,” Horton said. “When I did get that sack, it definitely boosted my confidence going into this week and knowing I can beat these tackles. I knew I could beat them before, but it gets me even more confident.”

The cornerback and safety positions opposite sophomore cornerback Nickell Robey and McDonald have proved almost patchwork in the last two seasons, as USC has shuffled numerous players through spots.

After all, teams will continue to shy away from Robey’s and McDonald’s territories and instead test their counterparts until other players in the secondary prove they possess similar playmaking ability.

Junior cornerback Isiah Wiley, after predominantly playing special teams this season, will assume the role of starting cornerback opposite Robey, at least until redshirt sophomore cornerback Torin Harris returns from a shoulder injury. Listed at 6-foot-1, Wiley, who registered five tackles and one pass break-up against Cal, offers a more physical complement to the 5-foot-8 Robey, and will likely guard Notre Dame’s elite wide receiver Michael Floyd, who is listed at 6-foot-3.

“I thought I played well, but I could have done a couple of things better out there,” Wiley said. “Once I got more reps, I started reacting faster. Starting off, it was almost like a shock to my system because I’m used to playing with athletes who aren’t as good as me in junior college, but once I got here, all of the athletes are good.”

Junior safety Jawanza Starling, who has sometimes struggled with tackling — notably against Arizona State on 70-yard touchdown run by running back Cameron Marshall — was praised for what Kiffin termed his “best game as a Trojan” against Cal.

“I left one, if not two, interceptions out there,” Starling said. “I still got room to improve a bit. You can’t be satisfied with just one game. Every week I’ve gotten better at understanding my responsibilities and my role. Wherever I am, I still need to make plays. Not having any missed tackles was big for me.”

Despite looking impressive at times this year, the defense understands it needs to get better, starting  Saturday against the Fighting Irish.

“We have to make sure the younger guys realize the importance of this tradition and make sure that there is a sense of urgency this week,” Horton said. “It’s a huge game. [Notre Dame] beat us last year in the Coliseum. I think a lot of people were embarrassed after that game, so we have to go up and make plays this weekend.”