Chargers linebackers Korey Toomer and Nick Dzubnar show their stuff against 49ers

Playing middle linebacker in new Chargers defensive coordinator Gus Bradley’s 4-3 scheme is both mentally and physically demanding.

First, you get the play call from a coach and relay it to teammates in the huddle. Then, you have to read the offensive set and, if necessary, adjust the defense like a quarterback calling an audible at the line of scrimmage.

After the snap, you need the dexterity and strength to shed a blocking lineman and tackle a speedy running back and the quickness to drop into pass protection and cover a bigger tight end.

Third-year pro Denzel Perryman was expected to fill the role this season until he suffered a left ankle injury in the Aug. 13 preseason opener that will sideline him for two to three months, leaving Korey Toomer and Nick Dzubnar to compete for the starting job.

As the Chargers prepared for Thursday night’s preseason finale against the San Francisco 49ers, a 23-13 loss at Levi’s Stadium, coach Anthony Lynn stressed the need for Toomer and Dzubnar to focus more on their physical play.

“Those guys, they’re thinking a lot,” Lynn said. “I’d like to see them free up and play, just turn it loose, play faster.”

Toomer appeared more confident, more active and more in command of the defense while playing most of the first half Thursday night, directing traffic in the box while freeing himself up to record three tackles — two for losses — one sack and one quarterback hit.

Toomer read a reverse and tackled Victor Bolden for a four-yard loss on San Francisco’s first possession. Later in the first quarter, on a third-and-12 play from the Chargers’ 34-yard line, a blitzing Toomer sacked quarterback C.J. Beathard for an eight-yard loss, forcing a punt.

The Chargers held the 49ers to eight yards on 13 plays in the first quarter. Toomer was on the field for Beathard’s 62-yard touchdown run midway through the second quarter but was covering a receiver on the opposite side of the field and couldn’t backtrack in time to prevent the score.

“I’m jelling with the guys, getting more comfortable every game, every step of the way, and that’s a good thing,” Toomer said. “I’m understanding what the coaches are asking of me, I’m understanding my teammates and what they want and how we’re gonna play the fronts.”

The 6-foot-2, 235-pound Toomer, who played college ball at Idaho, was a fifth-round pick of Seattle in 2012 and spent two seasons on the team’s practice squad.

He was primarily a special-teams performer for Dallas, St. Louis and Oakland in 2014 and 2015 before taking a big leap forward with the Chargers in 2016, starting eight of 13 games and finishing third on the team with 71 total tackles, nine for losses, and one sack.

“It was an eye-opener for me in that I was able to show coaches I can play this game,” Toomer, 28, said. “I just had to slow my mind down. Right now, I’m training to be mentally stronger than I was three years ago.”

Toomer is more athletic and has more range in pass coverage than Dzubnar, and he appears to have the edge going into the Sept. 11 season opener at Denver.

“Korey is a very athletic linebacker who can get off the blocks and get to the ball,” Bradley said. “It’s just the pre-snap process that we’re working on with him.”

Though Toomer called plays Thursday night, weakside linebacker Jatavis Brown is expected to assume some of the play-calling and pre-snap adustment duties in the regular season, easing the burden on Toomer.

Dzubnar, the former Mission Viejo High and Cal Poly standout and self-described “special-teams demon” last season, played the entire second half Thursday night and had three tackles, one for a loss, and looked solid in coverage.

Dzubnar broke up a short pass over the middle intended for DeAndre Carter on a third-down play early in the third quarter. Late in the period, after quarterback Nick Mullens dumped a short pass to Joe Williams in the right flat, Dzubnar slipped a Tim Patrick block and tackled Williams for a five-yard loss.

“Nick is a very strong leader,” Bradley said. “He’ll get up, make the call, get everybody lined up and make plays, and he’s rarely out of position.”

mike.digiovanna@latimes.com

Follow Mike DiGiovanna on Twitter @MikeDiGiovanna