Entering Week 1 of the 2015 season, the Minnesota Vikings were preparing to face a new-look San Francisco 49ers defense — on Monday Night Football, no less — that had been decimated by free agency, retirement and off-field issues.

A favorite on the road, the Vikings entered San Francisco with ample momentum, yet they exited Levi’s Stadium deflated after scoring just three points in a 20-3 drubbing. They later admitted that the 49ers defense presented things they had not seen on film and were not expecting.

A similar situation faces the Purple on Monday.

This particular Week-1-Monday-night game is at home, which helps, but the Vikings aren’t sure, exactly, what they’ll be facing when they line up across from the New Orleans Saints defense, a unit that has been fairly criticized for its porousness over the past three years.

Football Outsiders charted the Saints’ defense the 11th oldest in football last year based on snap-weighted age (26.8). But injuries and departures have led to a major youth movement.

New Orleans was 31st in points allowed last year, 32nd the year prior and 28th in 2014. While the 2014 and 2015 teams were equally poor against the pass and run, the 2016 team actually moved up to 14th in run defense but sank to dead last in pass defense, leading to a third consecutive 7-9 finish for the one-time Super Bowl champs.

Football Outsiders charted the Saints’ defense as the 11th-oldest in football last year based on snap-weighted age (26.8). But injuries and departures have led to a major youth movement.

Twenty-seven-year-old cornerback Delvin Breaux is out with a leg fracture, 29-year-old defensive tackle Nick Fairley is out with a heart condition, 30-year old safety Jairus Byrd was released in February and 30-year-old linebacker James Laurinaitis retired. Suddenly the oldest player on the defense is 28-year-old pass-rusher Cameron Jordan.

“I think they obviously have a new group of guys,” said Vikings quarterback Sam Bradford, “so you go back and watch last year’s tape and you realize there are going to be some different faces out there.”

Those new faces will comprise a completely swapped out group of linebackers and cornerbacks.

Manti Te’o (26), A.J. Klein (26) and rookie Alex Anzalone (22) will likely start at linebacker. Meanwhile, the Saints will trust a 24-year-old and a 21-year-old at the corner spots with P.J. Williams and first-round pick Marshon Lattimore, respectively.

There’s also some talk that 21-year-old Marcus Williams could unseat 22-year-old Vonn Bell at safety. Youth for youth.

the Saints will trot out a defense with an average age of either 24.3 or 24.5.

Depending on whether it’s Williams or Bell, the Saints will trot out a starting defense with an average age of either 24.3 or 24.5. That would be considerably younger than Cleveland’s league-youngest SWA defense a season ago (25.1). Six of the Saints starters will be 25 and under.

For comparison, the Vikings were the third-oldest SWA defense in the NFL last year at 27.8 years of age. That included then-38-year-old Terence Newman. If Newman should end up starting in place of Trae Waynes on Monday night, the average age of starters would tick up to 28 — still one of the oldest defenses in the league, even with Danielle Hunter taking Brian Robison’s place. Without Newman, it sinks down to 26.7.

The Vikings defense is stout, but it’s also been on tape for the past three seasons. While head coach Mike Zimmer continues to attempt new wrinkles in an effort to make his defense more unpredictable, the Saints and defensive coordinator Dennis Allen will be showing their hand for the first time on Monday Night Football.

“That’s the unknown about a first game,” said Zimmer, “you never know, really. I have seen some change from last year to this year in the preseason on some of the things they’re doing defensively. So yeah, it can present a problem.”

“I’m sure they’ve evolved through the offseason and training camp,” said offensive coordinator Pat Shurmur. “There are certain things that we probably didn’t see in the preseason games.”

New Orleans has four former first-round picks on its starting defense, but the real catalyst will likely be Lattimore.

The Saints secondary arguably got much better without Byrd, who rapidly declined with the Saints after three Pro Bowl seasons in Buffalo. Byrd was ranked 46th amongst safeties last year by Pro Football Focus and remains unsigned heading into the new season. The secondary got stronger with the addition of Lattimore, one of four former first-round picks within the starting defense.

Lattimore, the 11th overall pick out of Ohio State, who rebounded from a minor knee injury in training camp, will be asked to defend either Stefon Diggs or Adam Thielen in his first career start.

“Really good corner, good coverage skills,” said Zimmer. “Gets in and out of the breaks — good hands.”

Vikings defensive coordinator George Edwards insisted that just because the Saints defense is young, it doesn’t mean they’ll be running a simple approach. New Orleans has been known in the past for a ‘big nickel’ defense that utilizes a safety as the slot corner. They’ve also hinted that they could move away from the 4-3 base defense and incorporate elements of a 3-4 with more blitzing linebackers.

“Even though they may be young, what have they become accustomed to working in the offseason?” said Edwards. “Each situation is a little bit different. I think some guys that come from different programs have more experiences in different systems. It’s all individually based on their experience that the guys have coming in.”

For what it’s worth, the Saints ranked third in scoring defense in the preseason, giving hope to the Bayou faithful that their team’s offeseason transformation might have paid dividends. On the other end, the Vikings overhauled their scuffling offensive line and brought in Dalvin Cook at running back, only to struggle mightily in the preseason with the starting unit scoring three points in 12 drives.

“I think the biggest thing going into this week is making sure we’re all on top of what we’re doing,” said Bradford. “Having the answers for what they present us, making sure we’re comfortable with our game plan, comfortable with our plays, so that no matter what they throw at us we’re able to go out there play fast and just be the aggressors.”

Listen to Sam Every Week on the Cold Omaha Staff Pod!