Missed opportunities

Rey Maualuga and his fellow USC defensive players spent the spring, summer and training camp focusing on one theme: creating turnovers.

After finishing no lower than fifth nationally in turnover margin in each of the previous five seasons under Coach Pete Carroll, the Trojans ranked 38th in 2006.

So when Maualuga returned an interception to the end zone in the season opener against Idaho two weeks ago, he thought USC’s turnover troubles were over. But officials ruled that the passer’s knee had touched the ground before he threw the ball, nullifying Maualuga’s takeaway.

“It was one of the greatest feelings I’ve ever felt,” Maualuga said of his sprint across the goal line. “The next thing I know, I’m looking at Coach Carroll as I’m running to the sideline and he’s like, ‘Go back! Go back! That’s not a touchdown.’

“I was hoping he would celebrate with me.”

USC went on to beat Idaho, 38-10, but defensive players were somewhat subdued after losing the turnover battle, 3-1.

The Trojans recovered one fumble but missed several chances for interceptions.

“We were just a hair from doing it,” Carroll said. “It would have been a perfect start. It would have been 21 points or more.”

On Saturday, after two more weeks of ball-hawking emphasis, top-ranked USC will face No. 14 Nebraska. Defensive players intend to decide the outcome by taking the ball from the Cornhuskers.

“When the opportunity comes you have to seize it,” said senior linebacker Keith Rivers, who dropped several passes against Idaho.

Before last season, USC thrived in creating turnovers.

In 2001, the Trojans tied for fifth nationally with a 1.27 turnover margin and finished 6-6.

They ranked fifth again in 2002 (1.38) and improved to 11-2 by capping the season with an Orange Bowl victory over Iowa.

In 2003, USC ranked second in turnover margin (1.54) and won its first Associated Press national title in 25 years. The unbeaten Trojans ranked first (1.46) in 2004 when they won the Bowl Championship Series title.

In 2005, USC finished second (1.62). The Trojans intercepted 22 passes and recovered 16 fumbles. Then came last season’s precipitous fall to 38th (.31). The Trojans had 11 interceptions and 11 fumble recoveries.

Cornerback Terrell Thomas said the decline, “had to do with teams trying to be conservative,” to keep the games close.

Nebraska provided a blueprint for cautious play in a 28-10 defeat at the Coliseum, and other teams followed suit.

“It was definitely different than years past in terms of what people were doing against us,” defensive end Lawrence Jackson said.

A switch from a 4-3 defensive scheme to a 3-4 hybrid that got more linebackers onto the field also might have affected USC. New clock rules also shortened games and reduced the number of plays.

This season, the Trojans reverted to the 4-3 scheme and the NCAA rescinded most of the clock rules, setting the stage for what USC hoped would be a dominant performance in the opener against Idaho.

Maualuga appeared to provide the spark with his first-quarter interception deep in Idaho territory.

“I was like, ‘Here we go. It’s time,’ ” Thomas said. “We were just talking about it the series before. . . . When it got [nullified] it kind of took the wind out of us.”

Defensive end Kyle Moore provided the only turnover when he fell on a ball that slipped out of Idaho quarterback Nathan Enderle’s hand.

Defensive coordinator Nick Holt was not discouraged, even though the Trojans recorded only two sacks against an overmatched opponent.

“The ball was all over the place -- we were knocking it down and we had our hands on it a couple times,” he said this week. “But we have to get after the quarterback a little better.”

USC faced Nebraska quarterback Sam Keller two years ago when Keller played for Arizona State.

The Trojans intercepted five passes in a 38-28 comeback victory.

Keller was a redshirt last season at Nebraska and has led the Cornhuskers to victories over Nevada and Wake Forest. The fifth-year senior has had three passes intercepted and the Cornhuskers have lost one fumble.

Thomas is hoping the Trojans can cause more.

“If our offense gets ticking like they did against Idaho and can make Nebraska pass the ball and not be conservative to try to keep the game close, then maybe we can force more turnovers,” he said.

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gary.klein@latimes.com