Leslie Frazier strongly suggested Monday that Jasper Brinkley will remain at middle linebacker in obvious passing situations, even though the guy who typically handles that job, Erin Henderson, has recovered from his concussion.

"The way Jasper is playing," Frazier said, "it's hard to take him off the field in nickel situations."

That declaration spoke volumes about a player who was viewed -- at least from an outside perspective -- as a liability in pass coverage at the start of the season. The Vikings defense as a whole has become a surprising catalyst to the team's 4-1 start, and Brinkley's steady play in the middle embodies that unexpected story line.

Brinkley was billed as a run-game thumper, his skill set better suited to pummel running backs near the line than defend receivers. That's still true, but given an opportunity to expand his role and play on passing downs in Henderson's recent absence, Brinkley hasn't buckled in coverage.

If anything, he actually looks comfortable in that capacity, which seems like a promising revelation, except Brinkley wants to debunk the notion that he's not an every-down linebacker.

"I knew I could do this the whole time," he said. "I never really gave it a second thought about what the outsiders had to say because I knew and the coaches knew. I just had to get out there and do it."

That's precisely the point. Nobody really knew what qualified as reasonable expectations for Brinkley because his résumé didn't offer much supporting evidence. He spent his first two seasons primarily as E.J. Henderson's backup and then missed the entire 2011 season because of a hip injury. The team essentially handed him the starting job this past offseason when it decided not to re-sign Henderson.

Whether that was a risky gamble or a clear indication of the organization's trust in Brinkley's development, the Vikings' decision has been rewarded in the short term. He had a career-high 13 tackles against Detroit on Sept. 30 and had another active game Sunday against Tennessee, finishing with five tackles, a forced fumble and a pass breakup.

Brinkley has provided the defense toughness in the middle, a physical presence against the run and an edgy attitude as someone who loves to pop opposing players. And he's given his coaches reason to leave him on the field on third down.

"He's really increased our confidence in his ability to handle that role," Frazier said. "He's grown. He's always felt like he could do it if we gave him the opportunity and he's showing that he's capable."

That's not necessarily an easy task in the Tampa-2 scheme. The middle linebacker is responsible for the deep middle in pass coverage, which often requires him to defend big, fast, athletic tight ends. Brinkley is built like a tank (6-1, 252 pounds) and relies on brawn, but he has displayed some anticipation and awareness in coverage, too.

One play against Detroit, in particular, highlighted his growth as a pass defender. He sniffed out a third-down pass to Calvin Johnson underneath, closed quickly and tackled him short of a first down.

"That's exactly what we're asking him to do in that instance," defensive coordinator Alan Williams said.

Now, Brinkley just needs to make those plays consistently to inspire even more trust and confidence in the coaches' minds. He looked a step slow and tentative in the first few preseason games, which he blamed on rust from his layoff. He has steadily improved since then and presumably will continue to make strides as he gains more experience.

"If you're comfortable playing that position, you're going to be able to handle it," he said. "Whenever you start feeling like you've got a lot of pressure on you, it's hard to play that way. I'm just playing right now, just letting the game come to me."

The Vikings are pleased with the results. Brinkley began the season largely as an unknown, a big question mark in the heart of the defense. Many, including myself, raised doubts about whether he could handle that job and avoid being exposed as a weak link, particularly in pass coverage. So far, he's proven us wrong.

"To be honest, I'm doing the same things since I first came in as a rookie," he said. "The outside people never knew, so I guess they just assumed or whatever. But you just have to go out and make it happen. I feel like to this point I've done that."

Chip Scoggins • ascoggins@startribune.com