USC’s Matt Barkley isn’t the complete package yet

USC goes into its scrimmage Sunday at the Coliseum with several starting positions up for grabs.

Quarterback is not one of them, but Matt Barkley is on the spot.

Coach Lane Kiffin is seeking an improved completion percentage from the third-year starter.

Barkley, who completed 62.6% of his passes last season, was 10 for 20 for 82 yards Monday in the first preseason scrimmage.

Barkley said this week that his decision-making was “light years ahead” of his first two seasons.

But after cornerback Nickell Robey intercepted a Barkley pass and returned it for a touchdown during practice Saturday, Kiffin said freshman quarterbacks Cody Kessler and Max Wittek were leading the team in completion percentage.

“That’s them being really safe and conservative and [Barkley] being aggressive at times,” Kiffin said. “We really want to see him complete the balls [Sunday] and come out of this [scrimmage] at 70% or better.”

Barkley will have an array of targets, though sophomore Robert Woods is not expected to participate because of an ankle injury that has sidelined him the last few days.

Woods is the No. 1 receiver and, based on his performance in training camp, senior Brandon Carswell appears to be No. 2.

So redshirt freshman Kyle Prater, junior Brice Butler, sophomore De’Von Flournoy and a freshman contingent led by George Farmer are competing for significant playing time when USC opens the season Sept. 3 against Minnesota.

The Trojans are scheduled to scrimmage a third time before the opener, but Kiffin said everyone other than Woods and Carswell must start to assert themselves.

“It’s all washed up in there,” he said. “These next two [scrimmages] are going to be very big for all those guys.”

The 6-foot-5 Prater, who redshirted last season because of injuries, was given a prominent role in the scrimmage Monday. The Illinois native caught six passes for 38 yards, but he also dropped a pass and said he had a mental mistake.

Asked what he was focusing on improving, Prater did not hesitate.

“Consistency,” he said this week.

Kiffin agreed.

“We were actually hoping he would be ahead of his game at this time . . . just from having a year of being here,” Kiffin said, “But then again he didn’t practice very much during that year.”

Quick hits

Fullback Rhett Ellison did not practice after receiving stitches in his thumb. . . . Sophomore receiver Markeith Ambles, whose academic standing will not be determined until summer session grades are posted, was not at practice. “I’m kind of getting the feeling that he’s not going to be eligible and we just don’t want any distractions,” Kiffin said. . . . Music blasts from speakers during practice, but Kiffin, whose tenure as coach of the Oakland Raiders ended in 2008 with owner Al Davis’ strange news conference, apparently is not vetting the playlist. One of the songs played Saturday was DJ Khaled’s “All I Do Is Win,” which features an appearance by Snoop Dogg delivering the line, “Al Davis said it best. ‘Just win, baby, win.’”

gary.klein@latimes.com

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