ALLEN PARK, Mich. (AP) — The Detroit Lions invested in their linebacking corps in the offseason, drafting former Iowa star Jack Campbell with the No. 18 pick and re-signing Alex Anzalone to a three-year, $18.75 million deal to bolster a position group that was shaky at times last year.

Linebacker play will be key to Detroit’s defense after it finished 29th against the rush and 30th against the pass in the 2022 season when the team finished 9-8.

Anzalone, the veteran in the room, said this week at training camp the linebacker depth is as deep as he’s seen it in his three seasons in Detroit.

“There’s five or six guys who can legitimately start in the NFL and have started in the NFL, obviously Jack (Campbell) hasn’t yet,’’ Anzalone said.

Campbell has continued to impress early in training camp, recovering a fumble during drills on Friday.

“He’s growing mentally, there’s just little details to the game that you see from spring to the first full practices. His details have gotten better, his communication has gotten better. He does not make the same mistake twice,’’ coach Dan Campbell said Friday.

With the first day of pads on Friday, Campbell said the bar is low for the rookies until they get adjusted, but his expectations for Jack Campbell remain high. Still it’s a big step from Iowa to the NFL.

“He’s going to be plenty tough and physical, but now here you go, first day of pads. You get in there with the ones a little bit — he and (Derrick) Barnes sprinkle in and out — you’re going against Jonah (Jackson), Frank Ragnow. It’s going to be a little different. It’s a little different than playing Indiana,’’ coach Campbell said.

Barnes, entering his third year, and Campbell, who is 6-foot-5, learn from each other. They’re pushing each other to earn a starting role.

“I give him advice anytime he asks me questions which is crazy because I remember asking Alex questions when I was a rookie and just as much as I can help that guy. He’s a very, very humble guy and that’s what I like about him,’’ Barnes said.

A starting role last season does not guarantee anything for this year.

Malcolm Rodriguez, a sixth-round pick who started 15 games last season as a rookie, has had a good camp so far.

Anzalone said veteran Jalen Reeves-Maybin is sometimes overlooked as a possible plug-in starter.

James Houston, in his second year, didn’t see action until Thanksgiving last year and then exploded with eight sacks in seven games. He finished second in sacks to Aidan Hutchinson who had 9.5 in 17 games.

Julian Okwara, in his fourth season, started in two games in 2022.

“Shep (linebacker coach Kelvin Sheppard) is always talking about competition, competition. It’s one of those things, we bring that level of expectation and competition out in everybody,’’ Rodriguez said.

The depth boosts the competition level.

“If you have the ability to play and you deserve to play, you’re going to play whether that’s starting or if it’s coming in for 20-30% of the snaps, you’re going to play,’’ Anzalone said.

NOTES: RG Halapoulivaati Vaitai and rookie safety Brian Branch returned to practice on Friday. … WR Jameson Williams, who injured his leg on Tuesday, remained out, along with safety C.J. Gardner-Johnson, who was carted off the field on Monday with a knee injury. Campbell said both are day to day. … The Lions signed WR Trey Quinn and waived injured WR Tom Kennedy who was hurt during Wednesday’s practice. Quinn played for the USFL Michigan Panthers.