Is a freshman already winning USC’s battle for defensive tackle?

More so than any departing USC player — more so than a lot of current players — the Trojans love to talk about Stevie Tu’ikolovatu, the 25-year-old defensive tackle transfer who became one of the defense’s best players last season.

Tu’ikolovatu is mentioned several times in interviews during spring ball.

One reason is that Tu’ikolovatu was popular in the locker room, a mellow, married man among rowdy teens. But the bigger concern: Tu’ikolovatu was an essential piece on the defense. And USC is still figuring out how to replace him.

The Trojans are deeper at defensive line this season. Defensive line coach Kenechi Udeze said that will allow him to deploy players at their natural positions instead of having to shoe-horn players into positions of need.

But he wouldn’t yet commit to saying this season’s defensive line will be better.

“We’ll wait and see,” he said. “If I knew that then guess what? I’d be running around with sparklers at practice.”

Whether the line improves will depend mostly on the defensive tackle position. Coach Clay Helton anticipates USC will use nickel defenses often next season, meaning the Trojans will often use only one defensive tackle. Here’s a look at the three players hoping to take over the role:

Josh Fatu

Fatu was the lesser heralded of USC’s defensive tackle transfers last season, a junior college player brought in to bolster the Trojans’ depth.

Now, after spelling Tu’ikolovatu at times last season, Fatu is the incumbent and was the de-facto starter when spring camp began. In the past week, though, freshman, Marlon Tuipolotu has begun to take the small majority of first-team repetitions.

“The best player plays,” Helton said. “Both Josh and Marlon are going to have to help us.”

Fatu doesn’t have the ceiling of Tuipulotu, but he does have experience. He spent two seasons in junior college before transferring last season. Now, he’s a senior with space-eating size, at 6 feet 3, 290 pounds.

Marlon Tuipulotu

USC’s biggest coup during the offseason was convincing Tuipulotu to flip from Washington. Of USC’s three main options at defensive tackle, he shows the most promise.

Tuipulotu is still 17 years old, but he is already listed at 6-3, 295 pounds, and his spring ascension bodes well for his playing time early next season.

He has earned effusive praise from USC coaches. Here is a brief sampling from, just from Helton:

“Extreme strength and quickness.”

“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.”

But there are periodic reminders that he is still young.

On Tuesday, Tuipulotu burst through USC’s offensive line and advanced within arm’s length of quarterback Sam Darnold. Then Darnold juked, Tuipulotu went flailing and Darnold had escaped far enough to gloat.

“Welcome to college, rook!” Darnold said.

Kenny Bigelow Jr.

Bigelow will celebrate his birthday on Friday. He’ll also have a celebration for a different milestone: One year since his latest surgery.

Bigelow is the biggest unknown on USC’s front seven. He was one of USC’s best recruits in the 2013 class, a five-star recruit according to many scouting services. But his resume is brief:

Redshirted in 2013. Tore ligaments in his right knee 2014. Played as a reserve in 2015. Tore knee ligaments in his right knee in 2016.

Bigelow recently participated in contact drills at practice, but he has not been cleared for full team drills.

“It just feels really good to knock some of this rust off,” Bigelow said Thursday.

Sitting out another season, he said, “Honestly, it just, it was terrible.”

Bigelow was expected to start last season before his injury required USC to land a transfer. His effectiveness this season is still an open question.

“Just his leadership will be valuable,” Helton said. “And I hope that confidence and that health comes back for him because he can be a dominant player when he wants to be.”

Bigelow said his limitations in practice were a precaution. Udeze was choosing to be optimistic about Bigelow’s ability to respond to knee surgery.

“Did it set Adrian Peterson back?” Udeze said.

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand