The Athletic recently had an exclusive opportunity to sit down, via video call, with Lions coordinators Aaron Glenn and Anthony Lynn for separate, approximately 30-minute film sessions. In them, they broke down the film of a few of Detroit’s key free-agent signings and how they fit the coaching staff’s schemes. The conversation that follows with Glenn is the first of a four-part series.

Ahead of the 2021 NFL Draft, Lions GM Brad Holmes made three key moves to begin resetting the direction of Detroit’s front seven: He traded for veteran defensive tackle Michael Brockers. He re-signed Romeo Okwara to a long-term deal. And he added linebacker Alex Anzalone via free agency.

Anzalone, 26, to that point had spent his entire four-year NFL career in New Orleans, where new Lions coach Dan Campbell and defensive coordinator Aaron Glenn were on the coaching staff. As with many of Detroit’s signings (or the Brockers trade), there was a level of comfort with Anzalone — a familiarity regarding what he’d bring to the locker room and what his strengths and weaknesses were on the field.

The Lions’ expectations for him also shed a little more light on how Glenn’s defense will operate.

In a recent Zoom conversation with The Athletic, Glenn expressed a desire for linebackers “who can move laterally,” as opposed to just being straight downhill defenders. Whether out of a 3-4 base or a four-man front, the Lions will ask their defensive linemen to crash gaps with enough explosiveness to keep the entire O-line occupied. Doing so would leave Detroit’s second-level defenders to “stack and fall back” — help ensure nothing gets through between the tackles but stay free enough to flow to the ball.

Those plans also explain why the Lions were so high on linebacker Derrick Barnes, whom they traded up to take in Round 4 of this year’s draft. Barnes could fill some of the same assignments as Anzalone, but he also could slot in behind Jamie Collins or even take edge reps.

“He’s explosive,” Holmes said of Barnes. “He can really run. He’s got long arms. He can shed blocks. He plays with tenacity. He has a background as a pass rusher, so he’s got the versatility to do a lot of different things and I think that that’s needed in today’s game.”

Up front, too, the Lions’ draft selections of Levi Onwuzurike and Alim McNeill mesh with how Glenn describes his possible defense. Those two rookies likely will play out of different gaps — McNeill as a nose tackle; Onwuzurike likely somewhere between a three- and five-tech. But, in either case, Glenn will utilize their athleticism to wipe out gaps and keep the linebackers clean.

“At a minimum,” Campbell said on SiriusXM NFL Radio, “we’re gonna get some good push out of Levi and McNeill and really force these quarterbacks to get pressure in their face.”

How will it all come together? What was the appeal of Anzalone, as the Lions approached him in free agency? In diving into Anzalone’s film, Glenn had the answers.