The defensive line in 2015 was again an area of strength for the Vikings, especially so before nose tackle Linval Joseph suffered a toe injury in late November. That group combined for 30 sacks in the regular season and helped the Vikings defend the run a little better compared to 2014.

While defensive end Everson Griffen made the Pro Bowl as an alternate after recording a team-high 10.5 sacks, Joseph was the biggest standout along the defensive line, even if he didn't get an invite to Honolulu. Joseph was arguably the NFL's best nose tackle in his second season here.

Next to Joseph on the inside, both Sharrif Floyd and Tom Johnson played well in spurts, though injuries to Joseph and Floyd meant that Johnson had to start eight games. He is best utilized as a situational pass rusher.

The fourth starter, veteran Brian Robison, played better in his second year under coach Mike Zimmer. But third-round pick Danielle Hunter recorded six sacks, one more than Robison, despite playing much less. His emergence could help put Robison's roster spot in jeopardy this offseason.

Those six players were the mainstays in Zimmer's defensive line rotation. Four others played sparingly throughout the season, most notably 2014 third-round pick Scott Crichton, who is officially a disappointment.

Most of key members of this position group will be back in 2016.

Vikings free agents: Nose tackle Kendrick Ellis and defensive end Justin Trattou are both unrestricted free agents and seemingly replaceable.

Level of need: Low. The Vikings are in good shape here, but they could look to bolster their depth in the draft, especially at nose tackle. Shamar Stephen, who surprisingly carved out a role as a seventh-round pick in 2014, missed most of the 2015 season due to injury and the Vikings did not trust Ellis to play a significant role in the four games Joseph sat out.

Stat that stands out: six — players aged 21 or younger who recorded at least six sacks in a season (since it became an official stat). Hunter, who turned 21 in October and was the NFL's youngest player in 2015, is one of them.

Burning question: Will Robison be back for his 10th season with the Vikings? He turns 33 in April, has a $5.1 million cap hit and must fend off Hunter for a starting job. The Vikings might be comfortable paying him what he is owed given his leadership and his ability to slide inside on passing downs. Or they could approach him about taking a pay cut like they did with veteran outside linebacker Chad Greenway in the previous two offseasons. Or they could just cut him, something Robison acknowledged as a possibility last month. But Robison still has a little left in the tank.

Check out the Access Vikings blog tomorrow for a look at the linebackers.