A makeshift offensive line is stressing out USC coaches

USC Coach Clay Helton plunked a football down just outside the goal line. USC’s offense lined up with heels almost touching the chalk. Helton calls it the “backed-up” drill: The offense tries to punch out from its own end zone.

Only on Tuesday, the defense was pushing the offense back. Quarterback Sam Darnold had to twist and turn to throw a ball away to avoid a safety. USC’s defensive line was plunging through gaps.

Watching the offensive line, Helton said, “You try not to pull your hair out.”

Of USC’s biggest concerns this spring, the Trojans have begun to find answers for all but one: the offensive line.

A spate of injuries has sidelined USC’s three returning starters, Nico Falah, Toa Lobendahn and Viane Talamaivao. Talamaivao underwent surgery Tuesday to repair a partially torn biceps, though “he should be ready for training camp,” Helton said.

The effect has been a makeshift line and a murky idea of how USC will replace tackles Zach Banner and Chad Wheeler and guard Damien Mama. Offensive line coach Neil Callaway has been forced to shuffle players into new positions. Chris Brown changed sides and positions, from left guard to right tackle. And young players have been thrust into first-team action. Andrew Vorhees, who was not old enough to vote in November’s election, has started at guard.

“We’re still working at it,” Callaway said.

Chuma Edoga has been a rare mainstay at left tackle, one of the few linemen who has not shuffled positions. His development will be key. Helton said Edoga’s “athleticism just stands out.” Now, he said, Edoga needs to add consistency.

Helton said Edoga has matured since last season, when he was ejected from a game for pushing an official.

Callaway, a more gruff, direct type, did not enthusiastically endorse the assessment of Edoga’s maturity.

“You’d have to ask Clay that,” he said. He added: “Chuma still needs to work hard. And he’s making progress, but he’s got a lot of work to do.”

The return of the three injured players should add stability. Lobendahn, who started at center last season before sustaining a season-ending knee injury, is expected to be fully back by fall camp.

Falah has a herniated disk that is not serious enough to require back surgery. He has participated in individual contact drills but has been kept out of full team drills as a precaution, he said.

The injury could force yet another positional change. Falah excelled at center after Lobendahn’s injury. The two were expected to battle in the spring, but Falah floated a different strategy in a meeting with the coaches and trainers last week.

“I had the idea, what if I played tackle?” Falah said. “Less stress on my back.”

Falah is used to change. He has played all five line positions while at USC. So he can empathize with the newcomers playing in unfamiliar spots.

“It’s tough on the young guys,” Falah said. “But they have to learn sometime.”

Burnett catches on

For the first time all spring, offensive coordinator Tee Martin had to use a second hand to count the incompletions intended for Deontay Burnett. Two passes in his direction fell to the grass. His tiny total of incompletions rose to six. He still has yet to drop a pass.

Burnett has been a reliable force atop a deep but unproven receiving group this season. After Saturday’s practice, Helton singled out Burnett before the team as “an example of what a Trojan should be.”

After some connections with Darnold, Helton said, the coaches were “all looking at each other going, ‘Whoa.’”

Behind Burnett, the field is crowded with a five-man recruiting class from a year ago. Velus Jones Jr., now a redshirt freshman, was the first to separate himself.

“He seems to have created an explosion play each and every day,” Helton said.

In high school, Tyler Vaughns had been the highest rated by most scouting services. At USC, he had been among the quietest until Saturday, when he made three diving catches while blanketed in coverage.

Helton called it “by far his best practice.”

Rookie impresses

At practice a week ago, defensive tackle Marlon Tuipulotu burst through USC’s offensive line and advanced within arm’s length of Darnold.

Then Darnold juked, Tuipulotu went flailing and Darnold escaped far enough to gloat.

“Welcome to college, rook!” Darnold said.

It was a reminder that Tuipulotu still has some learning to do — and that the 17-year-old has progressed way ahead of schedule.

Tuipulotu has already claimed a tentative hold on a starting tackle spot. He is still competing with two seniors, Josh Fatu and Kenny Bigelow Jr., who is coming off a knee injury. But Tuipulotu has been the revelation of spring camp.

Here is a brief sampling of how Helton has described him:

“He’s not a raw kid.”

“Just one of the more football instinctive kids that I’ve seen.”

“You don’t see too many 300-pound men with his athleticism and his quick twitch. It’s just evident on the tape. It shows up each and every day.”

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand