(This is the final installment of a series previewing Bills training camp, which opens Thursday. Today's installment deals with the defense).

      When Chan Gailey was an assistant coach with the Pittsburgh Steelers from 1994 to '97, he saw the havoc a 3-4 defense can cause.

     During that four-year span, the Steelers never ranked lower than sixth in defense and averaged 49 sacks per season.

     Is it any wonder Gailey made the 3-4 his defense of choice when he was hired as the Buffalo Bills' head coach?

     "Having been around it, I realize all the different looks that you can get from 3-4 personnel," Gailey said. "I thought that in looking at it, the diversity, I don't want to say overwhelming, but it was drastically different from the four-man front. I think it's the right defense for us."

     After nine years in the 4-3, the Bills are going back to the defense of their most glorious era and beyond. The 3-4 was the base defense Marv Levy employed during the Super Bowl years in the 1990s. Wade Phillips used the same defense as Levy's successor, and it finished sixth, first and third in the NFL from 1998 to '00. Buffalo first went to the 3-4 under Chuck Knox in 1979.

     The challenge with the latest conversion to a 3-4 is a roster built to play the 4-3. The Bills added some veterans with 3-4 experience (defensive end Dwan Edwards and linebackers Andra Davis and Reggie Torbor), and Gailey hired a defensive coordinator with a strong 3-4 background in George Edwards.

     Those things help, but players must adapt to their new and unfamiliar roles for the defense to work.

     Gailey was encouraged by what he saw during the offseason practices.

     "I think they are doing a great job mentally because it's very different," he said. "There are so many adjustments and changes that are in the works. It's not your old basic defense where you line up, here we come, you've got to stop us. It's a lot of movement, a lot of thinking, a lot of adjustment and I think our guys have done a nice job of picking it up."

Following a trend

     You can count on one hand the number of 3-4 teams at the start of this decade. This season, more than half of the NFL's 32 teams will use some form of the scheme.

     The reason? Success breeds copycats.

     Teams that use the 3-4 defense finished No.‚1 in the NFL in yards allowed the last four seasons and allowed the fewest points in three of the last four years. A 3-4 team has led the league in takeaways for three consecutive years and ranked first in sacks twice in the past four years.

     The Bills have finished 22nd or worse in defense five straight seasons. The last time they ranked in the top 10 was 2004, their only winning season this decade.

     The Bills have been especially poor against the run. Their No.‚30 league ranking undermined the NFL's second-best pass defense. In two games against the New York Jets, the Bills allowed a whopping 567 yards rushing.

     Based on its recent track record, the 3-4 could equate to a better run defense. Four of the five best teams against the run last season played the 3-4. Topping the list was Green Bay, which, by the way, was in its first year in the 3-4.

     "When you play it right, gaps are canceled," said Dwan Edwards, a key member of Baltimore's third-ranked defense in 2009. "Things happen sometimes, but if guys play with good technique there shouldn't be anywhere to run."

Understanding the 3-4

     The obvious difference between 3-4 and 4-3 defenses is there is one less defensive lineman and one more linebacker on the field. The three down linemen are responsible for two gaps in run defense, whereas 4-3 linemen generally play one gap.

     The nose tackle is a key to the 3-4. He must be stout at the point of attack because he is often doubled and sometimes triple-teamed. Ideally, you want a nose tackle with size, but it has been proven that smaller, quicker guys (Dallas Pro Bowler Jay Ratliff, for instance) can hold their own, which is why the Bills have confidence in 305-pound Kyle Williams. They also drafted 315-pound Torell Troup.

     The inside linebackers have to take on offensive guards at times, but if the nose man attracts extra blockers, one of the linebackers should be free to pursue the ball carrier.

     The Bills' outside linebackers have the toughest transition because all of them, with the exception of Torbor, spent their entire pro or college career at defensive end. Not only are they the primary pass rushers in the 3-4, they also must provide containment on the perimeter during running plays and be able to drop back into pass coverage.

     "This defense is night and day compared to what we did in the past," inside linebacker Paul Posluszny said. "The run fits, the coverages, the responsibilities, the terminology, it's all very different from what a lot of us are used to. It's a whole new way of doing things."

     The Bills' secondary will undergo some philosophical changes, too. In the Tampa-2 scheme preferred by former head coach Dick Jauron, the defensive backs played mostly zone. They will play more man to man in the 3-4.

     "In the 3-4, it's almost man out there all day," safety Donte Whitner said. "We might call it a zone coverage, but it might be man coverage and that's better because it gives guys the opportunity to play tighter on the wide receiver and get a chance to jump some of those balls and get their hands on something. And by taking some of those checkdowns and underneath routes away, it gives our pass rush more time to get pressure because the quarterback has nowhere to go with the ball."

     Ah yes, pressure. That is the hallmark of the 3-4. What Gailey likes most about the defense is it keeps teams guessing.

     "In the 3-4, you don't know if the two front side [defenders] are coming, the two back side guys are coming, the two outsides [linebackers] are coming or the two insides [linebackers] are coming," said Gailey, who indicated George Edwards will still use some four-man fronts in obvious passing situations. "You have to account for all of them on every snap, whereas in the 4-3 it's easier to identify those guys."

     "This defense is a lot more difficult to find out exactly how you want to go protection-wise," added Davis, who was part of Denver's seventh-ranked 3-4 defense last season. "Every protection has a different nuance to it, so you have to be able to adjust that protection to what the defense is doing. It's going to be a real chess match between George and the opposing quarterbacks."

Work in progress   

  Gailey admitted he decided to play the 3-4 before knowing if he had the right people to play the defense, particularly in the front seven. But he soon found out he inherited players with the intelligence and work ethic to grasp the concepts.

      The defense is far from a finished product. Gailey suspects there will be growing pains along the way. Although Green Bay had immediate success moving to the 3-4 last season, Kansas City struggled with the transition.

     The offseason workouts were productive, but once training camp begins, Gailey will get a better idea of how the defensive transition is going and where it needs to be.

     "We're still trying to figure out what the pieces are," he said. "It's a little early to start to say we're fitting this thing together. Let's get the pads on, let's play a little while, let's see who does what with pads on, then we'll have a better idea of what's going to really happen."

awilson@buffnews.comnull