NFL players often compartmentalize their season into quarters, much like an actual game. It’s a familiar concept that’s easy to digest in a marathon 16-game season.

The Vikings begin their second quarter Monday when they return to work after their bye. Players would prefer a later bye — thus avoiding 12 consecutive games without a break — but their overseas trip to London necessitated an early vacation.

They probably appreciated a mental timeout after an eventful first quarter. The Vikings have played only one true home game and one “home” game 4,000 miles from Mall of America Field. Three of their four games have been decided in the final minute. And quarterback Christian Ponder could be on the cusp of losing his job permanently.

At 1-3 following a 34-27 victory against Pittsburgh, the Vikings expressed optimism that their season is salvageable after a dreary start. Here are four areas worth watching as they begin the second quarter:


1. Quarterback shuffle

It will be shocking if Matt Cassel is not the starter against Carolina next Sunday. Cassel gave the offense a spark in relief of Ponder against the Steelers, and it’s hard to imagine Leslie Frazier not sticking with him, even if Ponder’s fractured rib is healed enough for him to play.

Ponder’s injury buys the team another game (or two, possibly) to see if Cassel can continue to direct the offense with efficiency and balance without having to announce publicly a quarterback change.

If Cassel plays well, he keeps the job. If he struggles and the offense sputters, Frazier can go back to Ponder without having undermined his status by announcing beforehand that Cassel was the starter. In that regard, Frazier has handled this situation perfectly.


2. Where’s the defense?

The Vikings are 1-3 despite ranking fourth in the NFL in scoring at 28.8 points per game. That underscores how poorly their defense has played.

The Vikings rank last in the NFL in pass defense, 29th in total defense, 29th in scoring defense and 30th in third-down defense.

The one bright spot has been their ability to create turnovers. The Vikings already have collected 12 takeaways, tied for third most in the league. That total includes seven interceptions. The defense produced only 10 interceptions all of last season.


3. Secondary needs help

The secondary looked like a major problem area before the season, and that’s proved to be true through four games. The Vikings are allowing 326 passing yards per game (worst in the NFL) and have given up 10 TD passes (tied for worst).

The cornerback position is the primary culprit. Chris Cook missed the Pittsburgh game because of a groin injury and has yet to prove he can stay on the field for extended periods. Josh Robinson looks lost right now, and backup A.J. Jefferson played zero snaps on defense against the Steelers.

Frazier indicated that the coaching staff would consider possible changes during the bye. The most logical option would be to replace Robinson with rookie Xavier Rhodes as the starter at left cornerback, and possibly slide Marcus Sherels into the slot/nickel role.

Rhodes has been the team’s best cornerback, but Frazier has preferred to play the first-round pick strictly in the nickel package. Frazier said that plan still gives Rhodes plenty of work — he’s played 71 percent of their defensive snaps — but Robinson’s continued struggles might force the coaching staff to elevate Rhodes’ role.


4. Peterson on track

Adrian Peterson ranks second in the NFL in rushing (421 yards) and has a league-best five touchdown runs. Peterson sounded frustrated the first few weeks as defenses committed extra defenders to contain him, displaying no real fear of the Vikings passing attack.

He rushed for a season-high 140 yards and two touchdowns against the Steelers, which coincided with a turnover-free, balanced approach with Cassel directing the offense.

If Cassel can make opponents respect the passing game, Peterson should continue to reap the benefits. The Vikings have enough playmakers — Greg Jennings, Jerome Simpson, Cordarrelle Patterson, Kyle Rudolph — that they should be able to punish teams that devise game plans solely around stopping Peterson.

That, in turn, should loosen things up for Peterson, who hit his stride in his MVP campaign midway through last season.