LOS ANGELES - If the Rose Bowl were the Trojan War, Daryll Clark would be Achilles to Southern Cal.

The Penn State quarterback is considered the most dangerous Nittany Lion, and the junior would appear to have a Homer-sized bull's-eye planted on him.

Against Ohio State on Oct. 25, Clark was knocked out of the game with a concussion. His backup, Pat Devlin, took over and led Penn State to a crucial 13-6 win.

Devlin, however, has left the team. And the Lions are without a tested substitute should a vicious Trojans defense drive Clark to the sidelines.

It is no secret that when Penn State meets the Trojans on Thursday in the Rose Bowl, Clark will be under siege.

"They're very aggressive, and they're going to find out how tough a quarterback is," Penn State quarterbacks coach Jay Paterno said. "I don't think there's intent. But football is a physical game."

Fifth-year senior Paul Cianciolo is the backup. Some, including USC coaches and players, said the Lions would likely move wide receiver Derrick Williams under center rather than toss a green Cianciolo to the wolves.

"We heard about [Devlin's] quitting," Southern Cal linebacker Brian Cushing said. "Their backup, I think, is Derrick Williams. Knowing that, you never know what we're going to do."

The Trojans' defense is tops in the country in fewest points and yards allowed per game, with 7.8 and 210.6, respectively. Some consider it one of the best ever. The unit is led by two consensus all-Americans - linebacker Rey Maualuga and safety Taylor Mays - and three seniors who will play in the Senior Bowl next month.

"They have exceptional talent, exceptional speed," Penn State offensive coordinator Galen Hall said. "You look at their defense and it doesn't have a glaring weakness."

While he expects to be under duress, Clark doesn't imagine that USC would increase its pressure for the sole purpose of thumping him out of his shoes.

"Even if we still had more quarterbacks, I think they would pin their ears back and blitz," Clark said "That's part of their game."

However, he added: "But they're real intense. Sometimes they hit late and let you know that they're there."

Said Jay Paterno: "Everybody knows the most important position on the field is quarterback. You knock the guy out of the game - I'm not saying that's what they're trying to do - but they're going to try and make you sore."

Cianciolo has been used sparingly during his four years. The only time he really ran the first-team offense was in 2006, against Michigan, after Anthony Morelli and Clark went down in a 17-10 loss. This season, he has completed 6 of 9 passes for 86 yards and a touchdown in mop-up duty.

"Paul's our backup," Hall said. "We can do with Paul anything we've done with Daryll. If the two of them go down, with Williams in there, we're going to have to slice some things off."

Williams, a high school quarterback, ran out of the "Wildcat" formation against Iowa and completed one pass. Still, there's only so much time he can devote to learning a new position.

"I don't think Derrick is Sam Bradford or anybody slinging the ball around," wide receiver Deon Butler said, referring to the Oklahoma quarterback. "I think he can still be effective back there, but we want Daryll."

Clark creates his own problems. He had an excellent year throwing the ball, completing 60 percent of his passes, and his running keeps defenses on their toes. Maualuga will likely be responsible for containing Clark.

"Guys have certain responsibilities, but we won't have him spying every snap," Southern Cal defensive coordinator Nick Holt said. "Ray has other things to worry about."

USC has had problems with mobile quarterbacks, but, as Holt said, who hasn't?

"Because of our team speed, you can hopefully chase this guy down," Holt said. "But they run a lot of misdirection, a lot of nakeds, a lot of reverses to negate your speed. So we have to be assignment-oriented."

Clark, meanwhile, has to be himself. He had a three-game slump late in the season and lost some confidence. But he bounced back in the season finale against Michigan State, completing 16 of 26 passes for 341 yards and four TDs.

"We've had confidence in the kid all along," Hall said. "He might have needed it more than we needed it in him. . . . He's tougher on himself than we are."

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Contact staff writer Jeff McLane at 215-854-4745 or jmclane@phillynews.com.