Like the line, Ballard is a potentially good mystery

How many defensive linemen with question marks does it take to fill out a four-man front?

With Everson Griffen already in the fold, and potentially competing for playing time, Minnesota drafted Christian Ballard, who was dumb enough to fail a drug test during the biggest job interview of his life. That's the important thing to consider here. Not that he was caught smoking, you'd be naïve to think the League doesn't have others. But Ballard showed up to the Combine and tested positive.

There are also questions about his drive and his consistent play. The 6-foot-4, 283 pound defensive tackle ran a 40-yard dash time (4.75) that was seven hundreds of a second slower than Kyle Rudolph's. Physically, Ballard has all of the tools to be an explosive defensive lineman on the inside, or a stout run-stuffing defensive end with some quickness.

It's between the ears that's concerning.

That's why Minnesota got such a good value in the fourth round. That's why no one picked Ballard in the first 100-plus picks.

Scouting reports on Ballard say he takes plays off and didn't have as big of an impact as he could have had.

The Vikings' brass said after the draft that Ballard had a second-round grade on their board. They must have seen past the potential character concerns and desire-to-play issues.

Both Leslie Frazier and Rick Spielman liked the versatility Ballard offered, being able to play both defensive tackle positions or defensive end — basically anywhere on the line that Jared Allen isn't playing.

I'd like to see Ballard get some time at defensive end on sure-bet running downs and move inside on passing downs. And if he puts on some weight and shows consistency, there's no doubt he can be a long-term starter at defensive tackle. Weirdly enough, Kevin Williams isn't getting any younger.

Although it does seem like yesterday the Vikings botched their pick and still ended up with the Oklahoma State product.

Ballard is one more enigma along the defensive line amidst a very confusing offseason. Minnesota has Jared Allen at one defensive end spot. The rest is up in the air.

Pat Williams may never wear a Vikings' uniform again. And if he does, it won't be until week five. His Williams-Wall counterpart will also have to sit the first four games.

If Edwards does leave as a free agent, Brian Robison and Griffen could compete to replace him. Ballard could see time at that end position too.

That's where Ballard fits in at this point — he's the ultimate backup plan for a complete unknown for the Vikings. He can play anywhere, and that's reassuring when Minnesota's whole plan can change at the drop of a dime.

The key will be if he can develop into more than just a situational player. At this point, he will be a backup. Minnesota might prefer a bigger body to play next to Kevin Williams.

But is it that farfetched, especially if Edwards bolts, to expect Ballard to serve as a physical base defensive end and platoon the position with Robison, who himself has yet to shake the stigma that he's just a "role player."

Everything could change — Griffen could make a big leap, Robison could show he can play the run and get to the passer and Ballard could do the same. Or all three of them could all just be average players, as each was picked in the fourth round.