Devin White acted "childish" — that’s his word for his early days at LSU last year.

He resisted and avoided learning LSU’s defense, the one coordinator Dave Aranda spent hours trying to get him to digest.

He was frustrated, too, at his position move. He wanted to return to running back, move away from this linebacker thing, where he had to read guards and tackles, call out plays and recognize formations.

His days as a high school running back at North Webster were so easy.

“You just get the play and go!” he said.

This was different, and he didn’t like it.

He soon learned what it meant: no playing time.

“You can’t put a guy like me in the game — young and without knowing everything,” he said Thursday in his first interview since arriving at LSU in January 2016.

“I had to learn,” the sophomore continued. “(Duke Riley and Kendell Beckwith) sat me down and talked to me. They were like, ‘Devin, you’ve got to know this stuff. Because when you’re in, we’re counting on you to know everything.’ ”

White started learning, began playing and, a half dozen practices into spring drills, is serving as LSU’s starting rover, one of two inside linebacker positions in Aranda’s defense. He’s playing alongside Donnie Alexander, the starting Mack.

They’re members of arguably the most critical replacement job this offseason. Beckwith, the Mack for the past three seasons, and Riley, the starting Rover last year, are gone. With them go 41 starts, 97 games of experience and 407 tackles.

Alexander and White combine for three starts, 48 games played and 88 tackles.

It’s why the two have spent much of this offseason in Aranda’s office. They represent LSU’s only two true inside linebackers on scholarship, with signees Tyler Taylor and Jacob Phillips arriving this summer.

Aranda joked about the team’s situation with coach Ed Orgeron during this offseason.

“You know we have more kickers on scholarship than middle linebackers?” Orgeron said Aranda told him.

“We were talking a couple of times (this offseason). ‘I hope we’re not in this situation again,’ ” Aranda said last month.

For Alexander and White, this represents “a great opportunity,” Aranda said.

Taylor and Phillips are expected to contend for a starting job, coaches have said, but they’ll have to beat out these two to get it.

White is well aware of this fact. And he's ready to help out, using the same method Riley used on him last year.

“He taught me like he wanted me to take his spot,” White said. “I really enjoyed that. He wanted to see me have a bright future. That’s what I’m going to do to the next guy. I’m going to teach them everything they need to know so they can play.”

In just his 15th month at LSU, White has already grabbed the reputation of a trash-talking, young leader, a guy not afraid to bark at veterans or his offensive teammates. For instance, he playfully shared words with running back Derrius Guice during interviews Thursday, and he even pumps up his less-vocal counterpart. Alexander is the quiet one.

“He kind of pushes me even more, even though I’m a senior,” Alexander said. “He puts it in my head every day that we’ve got to go out and be great because we’re the leaders of the defense, basically.”

As for Guice, he talks back. After all, these are two muscle-bound teens who collide often during scrimmages.

“At practice, I can tell you I’m helping him,” Guice smiled, “because I’m messing over him right now. So he better be ready come time for fall.”

White is ready now, he says, long past over his resistance to learning Aranda’s defense or that frustration with his position change. He signed as a running back, enrolled early last January and was moved to inside linebacker last spring.

Things didn’t begin to really click until the Missouri game, the fifth of LSU’s season. He made a third-down stop and dropped the quarterback for a loss — two plays that proved to him that knowing the defense really does work.

“I was new to defense. I never played in a big defense,” White said. “High school was just, ‘Make plays.’ Coming to college, you just can’t make plays.”

White is now playing in his old high school number, switching from No. 24 over the offseason to 40, but don’t mistake it — he’s not playing like his prep days. He’s leading this team like he did at North Webster, vocal, emotional and talking trash.

A certain former LSU running back is making sure he’s doing that. Leonard Fournette called White on Wednesday night.

“He asked me if I was being a leader on the team,” White said. “He was like, ‘Age doesn’t matter because when I was a freshman and sophomore that’s what was expected of me.’ ”

Follow Ross Dellenger on Twitter, @RossDellenger.