vikings/nfl

MANKATO - The Vikings depth chart lists a different player as the primary backup at each of the linebacker spots. Jason Glenn is behind Ben Leber at one outside position, and Heath Farwell is Chad Greenway's replacement at the other. The only place Dontarrious Thomas' name appears is as E.J. Henderson's understudy in the middle.

This is one case where the depth chart fails to reflect reality and certainly doesn't give Thomas his due. Entering his fourth season, Thomas is the main backup at all three positions.

It's a role that has kept him busy during training camp.

In addition to working some in the middle with the second team, Thomas also has received extensive reps with the first team in place of Leber. Leber returned Tuesday after missing time because of a calf injury, but Thomas still replaced him during some drills.

"He has done a great job," defensive coordinator Leslie Frazier said of Thomas. "He has had to play multiple positions, but he enjoys it because he wants to be on the football field. Wherever we can get him reps, that's what he wants. He spends the time studying so he can be acclimated to each position."

Thomas, 26, was asked to become the primary backup at linebacker last season when Mike Tomlin was hired by new coach Brad Childress and installed the Tampa-2 scheme. Tomlin became coach of the Pittsburgh Steelers, but Frazier is keeping that plan in place.

"You have to just hit the playbook," Thomas said of keeping up on the assignments for three positions. "One of the things I pride myself on is being a smart football player. I think a smart football player gets in and studies film and studies his playbook and gets with the coaches and asks questions."

Thomas isn't the only Vikings linebacker with position flexibility. Vinny Ciurciu and Glenn, for instance, are both working in the middle and on the weak side. But Thomas is the only one who can play all three spots; he also can play on passing downs and has the ability to slide into a role in a 3-4 look the Vikings have at their disposal.

Linebackers coach Fred Pagac said all this knowledge gives Thomas a clear advantage. "It helps you a bundle because you know where your help is at," Pagac said. "When you play a scheme defensively, you set it up that 11 people have responsibilities. If you take care of your responsibility and can't make the play, you've got to force it to where your help is at. That's the whole key to the scheme."

While Pagac said it's not uncommon in the NFL for a team to use one linebacker as its primary backup, Greenway admits he's impressed by what Thomas is doing.

"As many blitzes and stuff that we have going in right now it's very tough to decipher," he said. "For me, and I'm playing one position, it's hard enough. So for D.T. to be able to do that is very impressive. He's got speed to play any position, and he's physical enough to play any position. He's just a tremendous athlete."

Thomas did have the advantage of being familiar with this defensive scheme; he played middle linebacker in a Cover-2 at Auburn. He also became used to playing multiple spots during his rookie season in 2004 when he took snaps on the weak side and in the middle.

Pagac said he feels the Thomas he is watching this camp is an improved player.

"I've seen strides," Pagac said. "He's quicker to read ... he's building confidence. I think that's one that once he thinks he's as good as he is, he'll be a lot faster."

That's good news for Thomas, who just wants to earn the coaches' trust. "I want to give them confidence that if a key player goes down they don't have to worry about anything," he said.

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Judd Zulgad • jzulgad@startribune.com