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The Pittsburgh Steelers have successfully employed a 3-4 defensive scheme for more than a decade, but it wasn't until Bill Belichick's Patriots started racking up Super Bowl rings that the rest of the league took notice. Now, as teams prepare their rosters for the 2005 season, there could be as many as 10 of 32 defenses that utilize the 3-4 scheme exclusively, or feature a hybrid of it.

The Steelers and Patriots have been members of the "3-4 club" for several years now. The Jets, Chargers, Raiders and Texans are recent additions, while the Cowboys, 49ers, Browns and Dolphins are potential newcomers.

Two teams swimming against the current are the Falcons and Ravens, who made wise decisions to transition back to a 4-3 scheme because of personnel. There also was talk of the Broncos switching to a 3-4 scheme this fall. That, of course, was before they re-signed DE Trevor Pryce and added the entire 2004 Cleveland Browns defensive line during the offseason. With 10 defensive linemen boasting NFL starting experience, Denver would be crazy to make the switch now.

That brings us to the most crucial lesson of this discussion: The 3-4 defense isn't for everyone.

The 3-4 can be an extremely effective scheme, but only with the correct personnel in place. Not all teams that have the 3-4 alignment use a two-gap technique along the defensive front, but most do, including the standard-setting duo of the Patriots and Steelers.

Within that philosophy, the job of the interior defensive linemen is to clog up two gaps at the line of scrimmage. Instead of working to get up the field in order to disrupt, the two-gap player's role is to control blockers in order to close up running lanes. These linemen typically emphasize size and strength over speed and athletic. Ideally, the nose tackle will be a 330-pound behemoth. The two defensive ends have to be more athletic, but ideally will weigh in around 300 pounds and will look a lot more like DTs than DEs.

The inside linebackers can vary. Often, teams will have one bigger inside linebacker capable of stacking up over an offensive guard and one smaller, more athletic inside man who can cover more ground against the run and in coverage. The outside linebacker is more of a hybrid defensive end/outside linebacker. He must be big enough (ideally around 6-foot-3, 260 pounds) to hold his ground against the run, but also athletic enough to rush the quarterback and drop in coverage on passing downs.

Getting an interior pass rush is the only true disadvantage when comparing the 3-4 to the 4-3, because defensive linemen in the 3-4 aren't typically built for penetration purposes. Otherwise, for teams with the appropriate personnel and the experienced staff to coach it, the 3-4 is absolutely the route to take in the NFL right now.

The NFL is a copycat league, which is one reason the 3-4 has become the trendy alignment. But a better question might be, "Why has the 3-4 been so successful the past few seasons?"

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