The Detroit Lions are 4-0 because of their lethal offense. There’s no disputing that. Calvin Johnson is having an MVP-caliber season and Matthew Stafford has become a star in his third year. But for a team to win eight straight regular-season games (Detroit won its last four games of 2010), they must have a half-decent defense.

And the Lions defense is quietly hanging in there.

After years of getting killed on pretty much a weekly basis, Detroit’s D is ranked 11th in the league at the quarter pole of the 2011 campaign. Only two NFC teams — Washington and San Francisco — have surrendered fewer points than the Lions have. The last time they surrendered fewer points per game than this: 1993.

The key has been the stacked defensive line and an underrated linebacker corps. The front seven is loaded with talent, and their fairly constant pressure has compensated for a sub-par secondary. As expected, Kyle Vanden Bosch and Ndamukong Suh have been very effective up front, and Cliff Avril has been quite good as well.

Their nine sacks don’t blow you away on paper, but watch them play and you can see the pressure. Only three teams have been better this year at stopping opponents on third downs, which is a strong indication that the front seven is doing its job.

And I get the feeling they’re only going to get better. Part of the rationale for that belief is that Suh has actually been slumping a little early on. Once he gets his game back to where we know it can be, the Lions will see even better results. But a lot of it has to do with the impending debut of one Nick Fairley.

The No. 13 overall pick in April’s draft missed the first month of the season due to a broken foot suffered in training camp. But the highly-touted national champion from Auburn is set to return to the lineup Monday night when the Lions play their much-anticipated nationally-televised game against the rival Bears, according to “a source familiar with the situation” cited by’s Michael C. Wright.

While Lions head coach Jim Schartz insists that Fairley — if he plays at all — will only contribute marginally as a backup, it might not take long for the 23-year-old to get up to speed. He’s considered to be an extremely pro-ready prospect after recording 24 tackles for lost yardage in the SEC last year.

Expect Detroit to break him in the next two weeks against Chicago and San Francisco, just in time to unleash him for what could be a huge Week 7 matchup with Atlanta.