Derwin James one of many defensive additions who could be a difference-maker on the Chargers’ defense

Chargers first-round draft pick Derwin James stood in the end zone with the ball in his hands, his teammates sprinting toward him to celebrate his interception of Philip Rivers in a red-zone, 11-on-11 drill Wednesday during the second day of minicamp.

It was the play of the day.

Thursday, James turned his head as a reserve receiver sprinted downfield toward that same end zone, leaving the rookie safety shrugging his shoulders as if to say, “What just went wrong?”

There are ups and downs to be had for James — and it was evident during the Chargers’ three-day minicamp that wrapped up Thursday — but he managed to show enough to have people convinced about what matters most. Thanks to additions such as James, the stingy defense should be even better in 2018.

“I can’t tell the future,” defensive end Joey Bosa said. “But it’s looking like we’re going to have a good defense.”

The Chargers had a good defense a season ago, with Bosa and Melvin Ingram providing the juice off the edge, cornerbacks Casey Hayward, Trevor Williams and Desmond King blanketing receivers and safeties Jahleel Addae, Adrian Phillips and Tre Boston patrolling the rest of the field.

Only two other teams — the Minnesota Vikings and the Jacksonville Jaguars — were more difficult to score against.

But defensive coordinator Gus Bradley and his players knew there were areas where they could improve, particularly in run defense. The Chargers hope their draft, in which they took four defensive players in the first four rounds, will make a difference.

“I think we’ve got a good class,” Bosa said. “Obviously, the spotlight is on Derwin. Watching him move around and the type of body he has, he’s really rangy and a long athlete, and watching the way he covers ground, it’s really impressive to me. We’re going to have a good defense with the guys we’ve added, for sure.”

James is comfortable with his place in the spotlight. Coach Anthony Lynn said no player has had more reps at safety during minicamp than James, who is working to learn both safety positions.

“It wasn’t too much that I can’t handle,” James said. “I’m used to playing multiple positions, knowing what to do in different situations. It’s kind of the same here. They asked me to do more, and I can do it.”

But he’s not the only addition who gives the Chargers high hopes.

Fourth-round pick Kyzir White impressed coaches as he transitions from being a safety at West Virginia to a weakside linebacker as a professional.

“He’s another young man that stood out this spring in shorts,” Lynn said. “We’ve put a lot on his plate as well. He played safety in college, but he’s going to play linebacker for us. It’s a new position, but he’s handled it very well.”

The Chargers also have seen a lot from last year’s seventh-round pick, Isaac Rochell, who has been impressive since the first days of conditioning work this offseason.

“He’s not even the same guy,” Lynn said of the defensive lineman.

Thanks to a bit of a physical transformation, Rochell is in position to earn a spot in the defensive line rotation.

“I’ve always liked Isaac. I think he’s a great guy and he has the potential to be a good rush end,” Bosa said. “The jump he made is kind of unexpected. Seeing him out here with his hands, the way he’s moving, it’s pretty unbelievable. He’s doing a really great job.”

The new pieces in the defense will be called upon to make plays, just as James did Wednesday.

“I just made a good play,” James said. “I’m supposed to do that. That’s my job.”

The Chargers hope he and the other defensive additions are good at it.

Etc.

Rivers, defensive tackle Brandon Mebane and offensive tackle Russell Okung were all given the final day of minicamp off for being veterans. … With Rivers out, both Geno Smith and Cardale Jones were shaky on Thursday, but Lynn said he’s comfortable with the quarterbacks on the roster. “I feel good about the quarterback competition,” Lynn said. “I like the guys that we brought in. I look forward to seeing it play itself out.” … The Chargers won’t formally meet together as a team until training camp begins in late July.

dan.woike@latimes.com

Twitter: @DanWoikeSports