The Minnesota Vikings have signed former Panthers cornerback Captain Munnerlyn to a three-year deal, with details pending per Ian Rapaport.

Free agency seems to be going according to plan, and the Vikings are beginning to fill in every need except linebacker and quarterback—which is to be expected given the age of the linebacker depth (whom many are hopeful can start) and the general inability to grab a long-term quarterback option in free agency.

Munnerlyn resolves arguably the biggest weakness from the 2013 Minnesota Vikings defense, which is pass coverage from the slot position.

Josh Robinson had the majority of the slot coverage duty for Minnesota and did a frankly abysmal job, competing with Robert McClain of the Falcons for some of the worst slot coverage in the NFL. No single cornerback gave up more receptions per snap in coverage or yards per snap in coverage, marking Josh Robinson with the singular distinction of being the worst statistical slot cornerback in the league.

His Pro Football Focus rating ranks him 99th of 110 players, and his film showed that. Despite speed and quickness, Robinson could never get his footwork right in space, too quickly opening the gate and letting receivers behind him. In addition, he was late to react to receivers going into breaks and couldn’t read the field or the quarterback.

While Robinson was acceptable in coverage when he was placed outside, the new emphasis on passing in the NFL makes it impossible to have an adequate defense without a slot-specific cornerback who is good at his job.

Captain Munnerlyn is coming off of the best year of his career, and has had consistently fine play at the spot, although no one would mistake him for Leon Hall or Chris Harris, Jr.—perhaps the two best slot cornerbacks in the NFL today. Notably, Leon Hall played for the Cincinnati Bengals under Mike Zimmer, and perhaps Zimmer can turn Munnerlyn from good into great with some coaching.

The deal is relatively cheap, although a little more expensive than I like given that Corey Graham, a very good slot corner who played for the Ravens just signed with the Bills for an average salary one million dollars lower. Nevertheless, it is a team-friendly way to turn one of the biggest weaknesses on their defense into a relative non-issue.

Captain Munnerlyn’s Pro Football Focus grade was 11th of all corners last year, and he gave up league average statisics in yards per target, yards per snap in coverage and receptions allowed per snap in coverage. More importantly, he grew into his role after several seasons of relatively average play. A lot of that grade was due to his ability to stop the run, but it is more important to note that it was an outlier year for Munnerlyn. In coverage grades alone, Munnerlyn had struggled to beat the league average until this year (but was never significantly below average, maintaining consistency in reliable coverage).

Munnerlyn started out his career with the Panthers as a punt returner as well as cover corner, so he’ll potentially compete with or at least back up Sherels in that spot, though he hadn’t returned a punt this last year and only returned more than 30 punts in his rookie and sophomore years (2009 and 2010).

He is known to be a very able run defender and excellent blitzer who has some big plays to his name, with four pick-sixes in the last two years. His play picked up significantly after the Panthers front seven improved by leaps and bounds, which does bring into question the sustainability of his play, but he’s been generally reliable in coverage, especially with the ball in the air.

Munnerlyn is significantly better in zone coverage reading the quarterback than in man coverage reading the receiver, but he’s still a solid player to get to recover the hole the Vikings had in the spot. His size (5’9″) and weight (182 pounds) are the biggest concerns and a reason fans should expect him largely to be a rotational player ready to receive significant snaps than a starter on the outside of formations.

When he was drafted from South Carolina in the seventh-round of the 2009 NFL draft, he had just come back from a Combine whose 40-yard dash time (4.51) was much slower than people might have expected given his on-field speed, but he was praised for his general agility and fluidity, two qualities he retains now.

The biggest question is how he’ll deal with the fact that all of the big receivers in the division—6’5″ Calvin Johnson, 6’4″ Brandon Marshall, 6’3″ Alshon Jeffery and 6’3″ Jordy Nelson—have increased their snaps from the slot position in the past few years and are more than comfortable playing slot routes from inside the numbers and tight to the formation. To Munnerlyn’s credit, he is not deterred by big bodies or physicality and relishes the contact.

Vikings fans may remember his aggressive play and personality against Percy Harvin from last year:

Antoine Winfield did a very good job against those big receivers with one or two notable exceptions in those cases, but Robinson, an inch taller than Munnerlyn, could not deal with their physicality and adeptness at the catch point. It helps that Munnerlyn has excellent timing, good hands and a superior ability to track the ball, but it should remain a concern until he can prove otherwise, as he struggled with size in Carolina.

All told it’s a good signing for the Vikings as he is a slightly-above-average corner improving from one of the worst players at his position.

There’s a good chance that Josh Robinson will have to compete for an outside spot against a potentially re-signing Chris Cook (there has been little said about his situation, but the 49ers were briefly interested in signing him) or a mid-to-high round draft pick. It’s an extremely deep draft for cornerbacks, which is good for the Vikings, who have not really resolved the position anyway.

Others who could potentially start outside include Shaun Prater, a player familiar with Zimmer as a former Bengals corner who signed with the Vikings partway through the season and shined in limited snaps.

Marcus Sherels, who recently re-signed, should be expected to be the primary backup option in the slot while Robert Blanton moves back to safety.

The Vikings are progressing well.