Johnson has right number in scrimmage

The USC bookstore has racks of jerseys for sale bearing Nos. 10 and 58.

Quarterback John David Booty and linebacker Brian Cushing wear 10 and linebacker Rey Maualuga wears 58.

Savvy speculators, however, might be wise to check out the discount rack, where No. 8 jerseys are deeply marked down because Dwayne Jarrett has gone on to the NFL.

Freshman receiver Ronald Johnson now wears No. 8, and he showed Sunday night that he could be a future star with two long kickoff returns and a short touchdown catch during the Trojans’ scrimmage at the Coliseum.

Johnson had kickoff returns of 53 and 52 yards and hooked up with freshman quarterback Aaron Corp on a nine-yard touchdown.

Freshman Joe McKnight returned a punt 74 yards for a touchdown against the service team on a night that featured few highlights. McKnight finished with 120 all-purpose yards.

“Overall it was raggedy. I don’t think we were nearly as sharp as we like to be,” Coach Pete Carroll said after the 78-play scrimmage, USC’s first in preparation for the Sept. 1 opener against Idaho.

Not surprisingly, the defense looked ahead of the offense when the first-team units were on the field.

“That’s to be expected,” said junior defensive back Josh Pinkard said. “We have a lot of experienced guys, and it’s usually like that after the first week.”

Senior running back Chauncey Washington ran for 78 yards in his only carry, sophomore Stafon Johnson gained 51 yards in three carries and freshman Broderick Green gained 14 yards in eight carries.

Booty completed seven of 14 passes for 53 yards and two short touchdowns to tight end Fred Davis and split end Patrick Turner. Mark Sanchez was four for eight for 29 yards with an interception.

Corp was four for four for 49 yards, and Michael McDonald was one for two, including a 50-yard touchdown pass to Cooper Stephenson.

David Buehler kicked a 49-yard field goal. Freshman linebacker Malcolm Smith and junior linebacker Kaluka Maiava each had five tackles.

Receiver David Ausberry no longer toils for the service team.

Not that he minded last season’s grueling and relatively anonymous work.

The 6-foot-4, 225-pound Ausberry relished preparing the Trojans’ defense for opponents, especially the extensive work against first-team cornerbacks and safeties. For his effort, and his vast improvement, he received an award and an ovation at the team’s postseason banquet.

Ausberry’s dynamic performance through the first week of training camp also produced cheers from coaches and teammates.

He has been particularly effective inside the 20-yard-line.

“He’s got great feet, he’s got loose hips,” USC receivers coach John Morton said. “Usually, big guys don’t have that kind of athletic ability.”

Ausberry had a diving reception along the sideline for 18 yards in the scrimmage.

USC annually woos recruits with promises to compete for playing time as freshmen.

But after spending training camp and the first few weeks of the season overwhelmed by the demands of the Trojans’ complicated passing game, Ausberry said he was glad that he was a redshirt in 2006.

“It was more of a relief because I knew I had more time to develop physically and mentally,” he said. “Now, I can read defenses better, I can run my routes better.”

Absorbing, and handing out, physical punishment against the first-team defense also prepared him for this season.

“No one hits harder than our guys,” he said.

Junior cornerback Cary Harris did not scrimmage because of a sore hamstring, Carroll said. . . . Jim Abbott blocked two punts. . . . USC players attended the AVP Manhattan Open beach volleyball tournament after the morning walk-through.

gary.klein@latimes.com