Chart: Vikings defense at a glance

RAISING THE BAR

The last Viking to excel at middle linebacker was a guy named Henderson. E.J., that is, who was a Pro Bowler in 2010 after delivering 105 tackles, three interceptions and a forced fumble. Now it's little brother Erin's turn to make noise in that role after spending the past two seasons as the weakside starter. Erin gained experience playing middle linebacker in nickel packages last season and now must take another big step forward in a full-time role. He'll need to emerge as a galvanizing leader in the huddle and a disciplined playmaker when the ball is snapped. His eagerness to be a difference-maker must be balanced by a patience to avoid trying to do too much. Oh, and cut the references to Erin following in E.J.'s path. The younger Henderson profoundly appreciates his brother's influence on his career, but … "You get to that point," he said, "where you're like, 'OK, this is Erin out there making plays. So give Erin some credit for what Erin is doing.' It doesn't always have to come back to the big brother thing."

STAR WATCH

Plenty of intriguing questions face Jared Allen heading into the regular season.

Is he again fully healthy after offseason surgeries to repair a torn labrum in his left shoulder and a meniscus issue in his right knee? If so, can he again make a run at the single-season sack record? But perhaps most intriguing with Allen is the question of whether this will be his final season with the Vikings. He's 31 and a 10th-year veteran with an expiring contract that will pay him more than $14.2 million in base salary this season. Then what? If Allen continues to be a Pro Bowl-level force, will the Vikings be able to afford the steep asking price it likely will require to keep him around? And if Allen's play shows significant drop-off, would the team be able to competitively afford to retain him on a principle of loyalty? General Manager Rick Spielman has made a point to shape his plans with younger and cheaper talent whenever possible. That could leave Allen out of the equation when his contract expires in March. Allen insists he'll deal with all business logistics after the season ends. So that leaves 16 regular-season games and a possible playoff appearance for Minnesotans to truly enjoy Allen's edge rushing tenacity and calf-roping sack celebrations.

THE X FACTOR

Harrison Smith's rookie tally: 79 solo tackles, 50 assisted tackles, 13 passes defensed, three interceptions — two returned for second-half touchdowns in seven-point Vikings victories. "He played with a controlled reckless abandon from my standpoint and wasn't afraid to take chances," coach Leslie Frazier said. Smith's aggressiveness is contagious. More important, he is rarely out of place, fueling the defense with his instincts, swagger and ability to play, in Frazier's words, with "no fear of failure."

THREE QUESTIONS

1 Can coordinator Alan Williams tap into his defensive line depth to develop a harmonious rotation, specifically at under tackle, where Kevin Williams (33 years old and six times a Pro Bowler) is expected to split time with top draft pick Sharrif Floyd?

2 What is the next step for Everson Griffen, still not a starter but entering a contract year as an explosive and versatile force who was a menace all throughout training camp?

3 After a preseason that saw the Vikings eyeing Marvin Mitchell, Desmond Bishop and Tyrone McKenzie at weakside linebacker, can a dependable, productive, long-term starter be found?