During USC’s 2011 Pac-12 road opener at Arizona State, the Trojans watched running back Cameron Marshall rip off a 70-yard touchdown run on just the fourth play from scrimmage, giving the Sun Devils an early 7-0 edge.

The scoring play would propel Arizona State to a 43-22 win at Sun Devil Stadium.

More than a year later, Marshall’s run also serves as a reminder of what was a glaring problem for USC in its first two seasons under coach Lane Kiffin: giving up the big play.

In 2010, the Trojans, on average, gave up 5.91 yards per play, placing them 90th among Football Bowl Subdivision teams. And in 2011, that mark dipped just slightly, as they surrendered 5.4 yards per play — good for 58th nationally.

Through five games this season, though, No. 11 USC has displayed noticeable improvement in this regard.

“We’re not giving up as many explosive plays as we did the first two years -— definitely in the passing game,” Kiffin said.

Of the 12 touchdowns the team has allowed in 2012, just three have come on plays of more than 20 yards. And in terms of yards per play, USC stands 22nd among 124 FBS teams, allowing 4.73 yards per play.

“We’ve made teams have to work and that’s why the scoring has been lower,” Kiffin said. “Guys have had to work to go down the field and a lot of times the offense screws it up.”

The numbers indicate as much. USC is giving up 19.4 points per game, roughly seven fewer than at this same point a season ago.

But the Trojans’ third-year coach is reserving judgment for now.

“You have to be careful of the stats and who you play and all that stuff,” Kiffin said. “We have not played the quality of quarterbacks that we had played in the previous two years to this point. Before we make this statement ‘Boy, we’ve improved so much on defense,’ we got to make sure we look at the whole thing together.”

USC had faced Arizona State quarterback Brock Osweiler and Arizona signal caller Nick Foles through this point last season. Both were selected in April’s NFL draft: Osweiler in the second round (57th overall) by the Denver Broncos and Foles in the third round (88th overall) by the Philadelphia Eagles.

Quick hits

— Kiffin announced during his post-practice news conference Wednesday that sophomore safety Josh Shaw has taken reps at the cornerback spot during practice this week.

— USC will practice for the final time Thursday before traveling to Seattle on Friday for its game against Washington at CenturyLink Field on Saturday night.

— USC has sold out its Oct. 20 game against Colorado, the school announced Tuesday. This will be the second home sellout this season. The Trojans’ season opener against Hawaii was listed as a sellout and so are two remaining games: Nov. 3 against No. 2 Oregon and Nov. 24 against No. 7 Notre Dame.