Former USC running back Justin Davis hitting his stride with Rams

The choice, based on the roster, seemed somewhat perplexing when Justin Davis chose to sign with the Rams as an undrafted free agent.

The former USC running back knew that Todd Gurley was the starter and that the team had signed Lance Dunbar as a free agent. Malcolm Brown and Aaron Green also were on the roster.

Where was the opportunity?

Davis did not worry.

Through offseason workouts and training camp, he said he focused on running hard, catching the ball and learning pass protections while also working to impress on special teams.

And he appears to be reaping some benefit.

Dunbar, who played five seasons with the Dallas Cowboys, was sidelined for most offseason workouts and has not participated in training camp drills because of a knee injury. His absence has enabled Brown to ascend to the backup role.

That leaves open a possible competition for the third running back position if Dunbar cannot return.

“I have to make sure I’m in a spot where I don’t miss a beat,” Davis said.

Davis has looked sharp at times during team drills, hitting holes with quickness and catching the ball well.

“I’ve been very pleased with him so far,” running-backs coach Skip Peete said. “He’s done a good job in both the running game and pass-protection game, and he’s surprised me as a receiver coming out of the backfield.”

Davis rushed for 2,465 yards and scored 21 touchdowns at USC. He is listed at 6 feet 1 and 198 pounds, but he appears substantially larger than he did in college.

“I really made it my No. 1 priority to get bigger,” he said, noting that NFL players hit harder and that he would be practicing against players such as Rams middle linebacker Alec Ogletree every day.

Unlike recent years, when rosters were trimmed to 75 from 90 and then to 53, NFL teams this season will carry 90 players and then cut down to 53 after the fourth preseason game. They also can retain 10 practice-squad players.

Davis must continue to perform at running back and prove his value on special teams to earn a spot.

“I’m trying to get into extra [special teams] film, because special teams is the quickest way on the field,” he said. “So I’m trying to master my craft, trying to do everything possible to get better at that.”

Right-side shuffle

Rob Havenstein, the starting right tackle the last two seasons, was moved to right guard during the offseason.

Jamon Brown, who played guard the last two seasons, appeared settled at right tackle after beating out the since-traded Greg Robinson during the organized-team activities and minicamps.

During Sunday’s short no-pads practice, Havenstein switched to tackle and Brown to guard, and coach Sean McVay said they would probably remain there at least part of the week.

“We feel really good about what Jamon and Rob have done on that right side, but with Rob’s history playing tackle and Jamon’s history playing guard, we also want to have contingency plans in place if one of them were to go down,” McVay said.

Sunday’s moves had been discussed even before last Saturday’s practice with the Chargers, McVay said.

“We’re just continuing to find whatever that best mix is for our five guys up front,” he said.

The Rams practice with the Chargers again on Wednesday. They play their first preseason game on Saturday against the Dallas Cowboys.

Brown said “cross training” at several positions gives the Rams flexibility. Havenstein agreed.

“Me and Jamon are open to any way we can help,” Havenstein said.

Etc…

Receiver Tavon Austin, who suffered a hamstring injury last week, did not practice. He has missed the last five workouts. … Rookie receiver Josh Reynolds (quadriceps) worked on conditioning drills …. Offensive lineman Andrew Donnal and receiver Bradley Marquez are not practicing because of knee injuries, McVay said. Donnal is expected to be sidelined at least a week, McVay said.

gary.klein@latimes.com

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