MANKATO, Minn. -- The biggest question surrounding the Minnesota Vikings when Mike Zimmer took over as head coach in January was the team's future at quarterback. The tallest task facing Zimmer when he accepted the job on Jan. 15 might have been remaking the Vikings' defense.

Zimmer's résumé as a defensive coordinator earned him the chance to work with a group that allowed more points than any in the NFL last season, and more than all but one defense in the Vikings' 53-season history. The coach began a detailed remodeling process almost as soon as he got the job, walking scouts and front-office members through what he'd need to succeed, and the trademark of his on-field work with players over the past two months has been an exacting adherence to details. The first concrete signs of progress came in the Vikings' preseason opener last Friday night, when the first-team defense forced a pair of three-and-outs against the Oakland Raiders. When he watched the film the next day, Zimmer saw some semblance of what he'd outlined for Vikings decision-makers months ago.

"It was a little bit like I envisioned this football team to look like. We didn’t make many mistakes on defense until later on in the ball game. We competed very well; we got up in people’s face on defense," Zimmer said. "I think that we are starting to develop a physical mindset with this football team. I like how we practice and the way we practice is showing up when the lights come on and we get ready to go play. We need to continue to practice at the same tempo, we need to continue to improve on the mistakes and we've still got a long way to go."

THREE REASONS FOR OPTIMISM

1. If Matt Cassel (or Teddy Bridgewater) can help the Vikings move beyond the quarterback turmoil of 2013, the team has enough weapons to catch up to the prolific offenses in the NFC North. Cordarrelle Patterson could be in for a breakout season in Year 2, Greg Jennings worked well with Cassel last season and Kyle Rudolph dropped 15 pounds in an effort to adjust his game to offensive coordinator Norv Turner's downfield passing game. The Vikings, of course, still have Adrian Peterson, and they're excited about the potential of third-round pick Jerick McKinnon, who could be the change-of-pace back Turner has typically had in his offenses.

2. First-round pick Anthony Barr should start at strongside linebacker, where he'll be featured as part of a defense that should be more aggressive than recent Vikings teams. While he was the defensive coordinator in Cincinnati, Zimmer sent five or more pass-rushers just 172 times last season (the seventh-fewest in the league), according to ESPN Stats & Information, but he'll bring pressure from more places than the Vikings did under Leslie Frazier. The Bengals, for example, blitzed a defensive back on 30 more snaps than the Vikings did last season.

3. General manager Rick Spielman has picked seven players in the first round of the past three drafts, assembling a core of young talent that could help the Vikings improve as quickly as it can develop. Third-year safety Harrison Smith is back from a turf toe injury that cost him half the season, second-year cornerback Xavier Rhodes is a good fit with Zimmer's press coverage scheme and Sharrif Floyd could become the Vikings' answer to Geno Atkins, the outstanding three-technique tackle Zimmer had in Cincinnati.

THREE REASONS FOR PESSIMISM

1. The Vikings will be counting on better depth in the secondary than they had last season, which means a number of unproven players will have to fill large roles. After the Vikings' experiment with Josh Robinson at slot cornerback backfired last season, he should be more comfortable on the outside, where he could start or play in the Vikings' nickel package once Captain Munnerlyn moves inside. But Robinson hasn't been asked to play much man coverage in his career, and the Vikings will need Rhodes to be their top cover corner in Year 2. They'll also need a starting safety to emerge alongside Smith, though the signing of 34-year-old Chris Crocker could help there.

2. There's little set at the linebacker position, where Chad Greenway is trying to rebound from the worst season of his career, Barr is developing as a rookie and Jasper Brinkley, in his second tour with the Vikings, is trying to hold off third-year man Audie Cole for the middle-linebacker job. In a scheme that leans on active linebackers, the position is one of the most unsettled on the roster.

3. Of course, there's the quarterback position. Cassel performed respectably at the end of last season, and seems comfortable in Turner's offense, but probably hasn't been among the top half of the league's quarterbacks since 2010. If he isn't faring well at the beginning of the season -- and the Vikings get off to a rough start against a schedule that includes dates with Tom Brady, Drew Brees and Aaron Rodgers by Oct. 2 -- how soon do the Vikings turn things over to Bridgewater? Whether they're counting on a veteran whom they signed last season as a backup or a rookie, the Vikings again begin the season as the only NFC North team with uncertainty about its starting quarterback.

OBSERVATION DECK

• The Vikings have used Barr as a defensive end in pass-rushing situations and could unveil more creative packages for the rookie this week. Zimmer has plenty of flexibility with his defensive fronts, considering Everson Griffen has played defensive tackle in the nickel package and Corey Wootton and rookie Scott Crichton have rushed from the inside. The Vikings have also toyed with dropping defensive end Brian Robison -- who began his college career as a linebacker -- into coverage in their nickel package.

• Zimmer wants safeties who can hold up in coverage, and he has unveiled a few nickel packages that feature three safeties and two corners. Considering how much time teams spend in nickel packages, safeties who can cover slot receivers and hold up against the run provide some additional flexibility. That's why Crocker -- who has played the past seven seasons for Zimmer in Atlanta or Cincinnati -- is back with him again.

• Depth at tight end could be a concern, especially early in the season; Chase Ford looked like he could be a solid receiving option behind Rudolph until he broke his foot before the start of training camp, and the Vikings cut promising undrafted free agent AC Leonard last week. Rhett Ellison has mostly worked as a run blocker so far in his career. Especially if Ford starts on the physically unable to perform list, the Vikings will have to hope Rudolph stays healthy a year after missing half the season with a broken foot.

• Running back Matt Asiata could carve out a role for himself in the Vikings' offense, especially now that Toby Gerhart is gone to Jacksonville and the Vikings need another running back who can hold up in pass protection. Asiata ran for 115 yards in the Vikings' final game of the 2013 season and has shown some ability as a downhill runner between the tackles.

• With punt returner Marcus Sherels nursing a hamstring injury, second-year receiver Adam Thielen has shown he can be a solid No. 2 option, returning three punts for 53 yards in the Vikings' preseason opener. As a receiver, Thielen has been one of the big stories in Vikings camp, displaying sure hands over the middle of the field and working well with Bridgewater in front of the same fans who cheered him at Division II Minnesota State, which hosts Vikings training camp.