INDIANAPOLIS — While Vikings coach Kevin O'Connell's focus is building an offensive playbook and roster to his liking, he doesn't want to lose track of a defense that could undergo even more changes in scheme and personnel in 2022.

O'Connell has entrusted veteran defensive minds Mike Pettine (assistant head coach) and Ed Donatell (defensive coordinator) to take over former coach Mike Zimmer's side of the ball. The two already started digging into the Vikings roster and sharing visions with scouts for what kind of players and traits fit the 3-4 defensive system they'll install this spring.

But when O'Connell eventually stands in front of the team, he wants to be knowledgeable about everybody's roles and not come across as a one-sided head coach.

"The best coaches I've been around, they have a baseline ownership of everything," O'Connell said. "I want to know the [defensive] calls that we're going to have. I want to know the secondary rotations, the fronts, mechanics of how we'll line up.

"You want to know when you stand up in front of the team as an offensive-minded head coach, those defensive guys and special teams guys have to know you're invested in what they're doing," he added, "and know you're invested in not only them as a player or as a roster spot, but how it all works and, really, ultimately that ownership we're asking them to have, I gotta have as well."

Defense was the backbone of the regime under Zimmer, who called plays for five straight top-10 scoring defenses from 2015-2019. At their peak in 2017, the Vikings fielded eight defenders who were past or future Pro Bowlers. But the defense will be changing more than its play caller, now Donatell, with many pending free agents and little salary cap space.

Of the nine Vikings defenders who played the most last season, six — linebacker Anthony Barr, cornerback Patrick Peterson, defensive tackle Sheldon Richardson, safety Xavier Woods, cornerback Mackensie Alexander and linebacker Nick Vigil — aren't under contract for 2022. General Manager Kwesi Adofo-Mensah is also hoping to "work with" defensive end Danielle Hunter on keeping him in Minnesota, presumably through a reworked contract.

Adofo-Mensah's task is to not only restart the pipeline for developing young talent, but also find immediate starters. He wants to build a durable defense, one that can withstand the injuries that undercut Zimmer's top-heavy groups the past two seasons.

"They had a lot of pieces in place on that defense," Adofo-Mensah said, "and they were a great defense for a long time, let me start off by saying that. This [Donatell] defense is great because it's designed to make it hard on the quarterback. We have a lot of players that can do that on all levels of the defense, at safety, at linebacker and defensive line.

"It's about taking the pieces you have and seeing where they fit in. You want to build a juggernaut. You want to put together the best team that has depth that can withstand injuries and be in it in a three-, four-, five-year horizon, and that's what we're trying to do."

That'll require financial tap dancing to fit talent under the salary cap, which is currently burdened by decisions from his predecessor. Rick Spielman pushed cap costs into future years for players like Barr and Richardson in last season's win-now effort. They are accounting for more than $11 million on this year's books despite not being under contract.

For now, the Vikings' division of labor among coaches is clear, with O'Connell focused on building his offensive playbook and depth chart as Donatell does the same on defense.

Remaking the defense might take a little more legwork for Adofo-Mensah and Donatell — the 65-year-old former Packers, Falcons and Broncos coordinator — considering how many new starters they could be seeking in free agency and the draft in the next two months.

"[Donatell] is absolutely submerged in learning our roster right now," O'Connell said. "Learning what we have, how these positions fit with a slight adjustment to the scheme. I think sometimes when you're calling things from a standpoint of 3-4 to 4-3 [front], that can be a little overblown with how much [two-linebacker] nickel defense you actually have to play in this league.

"But I know Ed is excited about a lot of our players we have here returning and the idea of adding some pieces that maybe fit exactly how we want to play."