The Detroit Lions lost defensive coordinator Aaron Glenn this offseason as he became the head coach of the New York Jets. The Lions promoted linebackers coach Kelvin Sheppard to defensive coordinator for the 2025 NFL season.

In a season full of injuries for the Detroit defense, the Lions placed seventh in points allowed and 20th in yards allowed among the NFL’s 32 teams in 2024.

Five of Detroit’s defensive starters for their season-opener weren’t around for the Lions’ playoff finale, and defensive end Aidan Hutchinson, defensive tackle Kyle Peko and linebacker Derrick Barnes missed as least 12 games apiece.

But Sheppard pointed to the youthful experience gained by the Detroit defense as he prepares for his first season as a coordinator.

“We have a young nucleus, a young core,” Sheppard said. “But somebody that jumps out at me — a Terrion Arnold. There is so much meat on that bone that he don’t even know.

“He called me a couple days ago, playing around. I said, ‘Where you at?’ ‘Down in Florida.’ I said, ‘You better enjoy it because when you get back the next time you see me, we getting to work, brother.’ And he’s like, ‘Oh, absolutely, Coach! I know how you roll!’”

Arnold joined Detroit from Alabama as the 24th selection in the 2024 NFL Draft. Even though he missed one game, Arnold was among the five rookies who played at least 900 defensive snaps in the 2024 regular season, and he played all 75 in the Lions’ 45-31 loss to the Washington Commanders in the second round of the NFC playoffs on Jan. 18.

In the first four games of the season, Arnold was flagged for defensive pass interference five times, defensive holding twice and a face mask once. In his remaining 13 games, Arnold was penalized three times, and because of a broken jaw suffered by former Auburn standout Carlton Davis, he played the most snaps at cornerback for the Lions this season.

“He’s got the right attitude,” Detroit general manager Brad Holmes said at the NFL Scouting Combine. “Again, he took some lumps early, had some aggressive penalties earlier. Like I said at the end of the season, I did think the water’s kind of calmed kind of halfway through.

“But he’s a very coachable player. He cares, he’s passionate, he’s prideful, so he’s going to do the necessary things. He wants to be a great player, we want him to be a great player, so I have no doubt that he’s going to continue to develop.”

Holmes credited former Alabama standout Deshea Townsend for his role in Arnold’s development as the Lions’ secondary coach.

“I thought Deshea did a great job with him,” Holmes said. “And, you know, I expected no different. But, yeah, I got a lot of excitement for Terrion.”

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Mark Inabinett is a sports reporter for Alabama Media Group. Follow him on X at @AMarkG1.