Progress, in fits and starts

Well, at least there was progress.

Early on, USC’s second scrimmage appeared to have all the makings of the first one, an uninspiring effort Tuesday that featured no points on the board from either quarterback vying to possibly replace injured starter Mark Sanchez.

On Saturday night at the Coliseum, Mitch Mustain’s first pass was intercepted and returned for a touchdown. Aaron Corp emerged unscathed stat-wise from his first series, then had a pass tipped and intercepted on the second.

But Mustain and Corp eventually settled down and the offense took some small steps toward productivity with the Aug. 30 opener against Virginia looming.

“Not as sharp as we’d like to be,” Coach Pete Carroll said.

The offense has two weeks to build on its good points and shore up its weaknesses.

The positive: Mustain passed for a touchdown and led two drives that resulted in field goals. Corp also led a touchdown drive.

The negative: Both are still struggling to play consistently well, a situation caused in part by an offensive line that remains a major work in progress. Running back Stafon Johnson and receiver Vidal Hazelton also fumbled.

Johnson (58 yards rushing and a touchdown in five carries) and Allen Bradford (37 yards in four carries) shined at times, but Carroll accurately described the running game as “a little hit and miss.”

So was the passing attack, but the Trojans will take it after cornerback Shareece Wright picked off Mustain’s first attempt and ran it back 23 yards for a touchdown.

“That was just a bad play on my part -- I got anxious on it,” said Mustain, who rebounded to complete six of 12 passes for 118 yards, including a 26-yard scoring pass to Travon Patterson.

Mustain’s touchdown throw came almost immediately after Corp opened the scoring by efficiently engineering a drive that culminated with Johnson’s short touchdown run. Corp finished 12 for 16 for 64 yards, but was sacked four times.

“I did some good things but I’ve got to get rid of the ball. I can’t take as many sacks as I did,” he said.

Meanwhile, as the two quarterbacks-in-waiting battled for an edge, Sanchez lofted passes behind the bench, eyeing a return for the opener.

Should be an interesting two weeks.

Scrimmage highlights

Offensive play of the night: Johnson breaks free for 46 yards down the sideline.

Defensive play of the night: Wright jumps a Mustain pass and returns the interception 23 yards for a touchdown.

Hit of the night: Bradford and cornerback Cary Harris collide head-on in the flat. Harris suffers a sprained shoulder.

Other hit of the night: A fan grabs an overthrown pass and sprints into the Coliseum stands. Jared Blank, assistant director of football operations, runs him down between the seats, holding him until security arrives.

Something special: Reserve kickers Jordan Congdon and Joe Houston combine for three field goals of 40-plus yards. Joe McKnight returns a kickoff 63 yards and a punt 56 yards.

Cover four

The defense was in a Cover 2 alignment with Wright watching for receiver Patrick Turner to run something short. When Turner angled outside, Wright jumped the route.

“I just played off my zone,” he said. “The ball came right too me.”

His 23-yard interception return for a touchdown on the first series of the scrimmage underlined USC’s depth in the secondary this fall.

Wright’s solid play from spring ball has carried into summer camp, where he and Harris have lined up most often with the first defense. They find themselves scrambling to beat out Kevin Thomas and Josh Pinkard for the starting spots.

“We’ve got to declare two starters,” secondary coach Rocky Seto said. “But all four of them are showing that they deserve to play.”

Depth is important at cornerback, where a sore hamstring or other minor injury can force a player out of the lineup. The Trojans could end up rotating all four players during the season.

Not that anyone likes to share time -- “Me, personally, I want to be a premier corner; everybody wants to shine,” Thomas said -- but the foursome seem to have accepted the notion of daily competition.

“You have to come out with the right mind-set,” Wright said. “Our goal is to make each other better and win games.”

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gary.klein@latimes.com

david.wharton@latimes.com