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The Buffalo Bills showed a season ago that when healthy, they have an offense that can run with the big boys of the AFC. The next step for head coach Chan Gailey is for the defense to catch up in his third season.

It's then no surprise that the Bills addressed the defensive side of things immediately after the conclusion of last year's 6-10 season. One day after wrapping up the campaign, George Edwards was fired as defensive coordinator and Dave Wannstedt was promoted to the position.

Wannstedt, who spent last season as Buffalo's assistant head coach and inside linebackers coach, is shifting the Bills to a 4-3 scheme, and the front office certainly gave him some new weapons. Former No. 1 overall pick Mario Williams and fellow defensive end Mark Anderson were signed as free agents and the Bills spent their first-round pick in April's draft on South Carolina cornerback Stephon Gilmore.

Buffalo is hoping those additions lead to an improvement of a defense that ranked 26th overall and 30th in scoring despite forcing a combined 31 turnovers, including 20 interceptions that tied for the second most in the conference.

Wannstedt said he believes the defensive improvement will start with the guys up front.

"If we can get a good rotation going and keep some guys healthy, that kind of sets the foundation for what we're trying to get done here," he noted. "There's going to be some transitions, there's no question about that."

An improved defense could certainly go a long way in helping Buffalo post its first winning record since 2004 and first playoff appearance since 1999.

Of course, the offense will also need to stay the course after an outstanding 2011 campaign. That isn't asking too much given that 10 starters are back, including playmakers Fred Jackson and Stevie Johnson.

Quarterback Ryan Fitzpatrick also returns after helping the Bills average 351.1 yards per game, the fifth-best total in team history since the league went to 16 games in 1978.

Fitzpatrick will keep himself in the forefront of the offense, leaving the likes of Jackson and Johnson to perform with less scrutiny.

"I want all of the pressure to fall on me so the other guys can just go out there and play," stated Fitzpatrick. "Me being one of the older guys in the huddle, especially with our skill players, I love taking the pressure. It takes it off of them. They are able to just go out there and play. My shoulders are big enough for that and that is something that I enjoy."

Below we take a capsule look at the 2012 edition of the Buffalo Bills, with a personnel evaluation and prognosis included therein:

2011 RECORD: 6-10 (tied 3rd, AFC East)

LAST PLAYOFF APPEARANCE: 1999, lost to Tennessee in AFC Wild Card

COACH (RECORD): Chan Gailey (10-22 in two seasons with Bills, 28-36 in four seasons overall)

OFFENSIVE COORDINATOR: Curtis Modkins (third season)

DEFENSIVE COORDINATOR: Dave Wannstedt (second season with Bills, first as DC)

OFFENSIVE STAR: Fred Jackson, RB (934 rushing yards, 39 receptions, 6 TD)

DEFENSIVE STAR: Mario Williams, DE (11 tackles, 5 sacks with Texans in '11)

2011 OFFENSIVE TEAM RANKS: 14th overall (13th rushing, 15th passing), 14th scoring (23.3 ppg)

2011 DEFENSIVE TEAM RANKS: 26th overall (28th rushing, 19th passing), 30th scoring (27.1 ppg)

KEY ADDITIONS: LT Cordy Glenn (2nd Round, Georgia), DE Mario Williams (from Texans), DE Mark Anderson (from Patriots), CB Stephon Gilmore (1st Round, South Carolina), QB Vince Young (from Eagles), WR T.J. Graham (3rd Round, North Carolina State)

KEY DEPARTURES: WR Roscoe Parrish (to Chargers), LT Demetress Bell (to Eagles), DE Shawne Merriman (released), CB Drayton Florence (to Broncos), ILB Andra Davis (free agent), OLB Reggie Torbor (free agent), CB Reggie Corner (to Jaguars), S Jon Corto (released), K Dave Rayner (free agent)

QB: After failing to make a name for himself early in his career, Fitzpatrick (3832 passing yards in 2011) has found a home in Buffalo and is coming off a career season in which he surpassed 3,000 passing yards for a second year in a row. He also upped his total for touchdown passes by one to 24, though he did get picked off a career-worst 23 times while starting 16 games for the first time in his career. Still, there is no doubt he is the Bills' starter after finishing fourth in the AFC in touchdown passes and completion percentage (62.0), while his 353 completions were the second most in team history. Who backs up Fitzpatrick is more uncertain, with Gailey to pick between holdover Tyler Thigpen and former Tennessee Titans starter Vince Young, who spent last season as a backup with the Philadelphia Eagles. Thigpen already has a grasp of the system, but Young could edge him out if he can find the early-career form that led to the Titans taking him third overall in the 2006 draft. Also expected to see time under center in wildcat situations is the versatile Brad Smith.

RB: Jackson (934 rushing yards, 6 TD, 39 receptions) was well on his way to a career year before a fractured fibula suffered in November ended his season after 10 games. He had already set a personal best for touchdowns in a season and his 1,376 yards from scrimmage trailed only Chicago Bears running back Matt Forte at the time of his injury. The Bills still saw enough out of the undrafted 31-year-old to give him a contract extension through 2014 this past offseason. Despite Jackson's injury, the Bills still led the AFC with an average of 4.9 yards per carry thanks to solid production from backup C.J. Spiller (561 rushing yards, 39 receptions, 6 total TD), the ninth overall pick of the 2010 draft. He logged 463 yards over the final five games of the season and averaged 5.2 yards per carry on 107 attempts for the year, scoring four touchdowns on the ground and two as a receiver. Spiller should see increased work this year in an effort to keep Jackson healthy. Tashard Choice was claimed off waivers from the Washington Redskins in late November and returns this year as a depth back. The Bills started a fullback just once last year, with special teams ace Corey McIntyre getting the bulk of the work there.

WR: Key to the Bills' offense is the chemistry between Fitzpatrick and Johnson, who in 2011 became the first player in team history to post consecutive 1,000-yard receiving seasons. His 76 grabs also made him the second player in franchise annals to notch at least 75 receptions in back-to- back years. It isn't all sunshine with the 26-year-old, however, who has shown a habit of headline-grabbing touchdown celebrations that often overshadow his production. Last season against the Jets, he imitated shooting himself in the leg in a dig at then-New York wide receiver Plaxico Burress' well-publicized jail sentence for carrying an unlicensed firearm in a Manhattan night club. Johnson was also benched for three quarters in last year's season finale after getting flagged for a post-touchdown celebration. The Bills are hoping he makes good on his desire to curb those antics after recently signing him to a five-year contract. David Nelson (61 receptions, 5 TD) was Buffalo's best producer from the wideout spot behind Johnson and should battle Donald Jones (23 receptions, 1 TD) for the No. 2 role. Derek Hagan and third-round pick T.J. Graham (North Carolina State) should also see time on the field.

TE: Fitzpatrick may have found his key red zone target in 6-foot-7 tight end Scott Chandler, who saw the most action of his four-season NFL career in 2011 and produced 38 catches for 389 yards. Chandler's six touchdown catches also matched a single-season franchise mark for a tight end, which he posted over 14 games. Second-year Marshall product Lee Smith, who stands 6-foot-6, appeared in 10 games a season ago and is mostly used as a blocker.

OL: The Bills' offensive line led the NFL with just 23 sacks allowed a season ago, despite injuries leading to shuffling at the center and left tackle spots. Though Buffalo returns five players who logged starts last year, the unit is not without some questions. The first is at the all-important left tackle spot, where Demetress Bell took his services to Philadelphia in the offseason. The position will be filled by 2012 second-round pick Cordy Glenn after the rookie edged out Chris Hairston, a second-year pro who started seven games while Bell was injured last season. Center could also see some problems if Eric Wood can't stay healthy. The 2009 first-round pick missed the final seven games of 2011 due to a knee injury that needed surgery, his second leg injury in the NFL. Those uncertainties make guards Andy Levitre and Kraig Urbik invaluable. Levitre opens 2012 as the starting left guard, where he began last season before logging three games at left tackle and one at center and then returning to his original spot to close the season. Right guard Urbik, meanwhile, handled the bulk of the work at center after Wood's injury and was spelled on the right side by Chad Rinehart. Right tackle Erik Pears was one constant, making 16 starts a season ago.

DL: If Wannstedt believes that the defense will driven by the front four, then the Bills have a chance at having one of the top units in the conference. It starts with Williams, who signed a six-year deal worth $100 million after logging 53 sacks with the Texans following his selection as the first overall pick of the 2006 draft. The former 3-4 linebacker was limited to just five games last year because of a torn pectoral muscle. Expected to rotate at the other end spot are Chris Kelsay (41 tackles, 5 sacks) and Anderson, who is coming off the second double-digit sack total of his career. He had 10 in 16 games with the New England Patriots, but could lose some snaps to Kelsay if he can't develop into more than a pass-rush specialist. Kelsay has 30 sacks in nine seasons with the Bills, often playing outside linebacker in the 3-4 scheme last year. Wannstedt also has the luxury of a pair of 300-plus defensive tackles who can pass rush and clog running lanes in Marcell Dareus (43 tackles) and Kyle Williams. Dareus, the third overall pick of last year's draft, logged 5 1/2 sacks -- the most for a Bills rookie since 2001 -- while Kyle Williams had the same number of quarterback takedowns in 2010 before missing all but five games last year due to Achilles surgery. Dwan Edwards (52 tackles, 2.5 sacks), an end last year in the 3-4, and Spencer Johnson (47 tackles, 2 sacks) back up in the middle. The Bills released former Pro Bowler Shawne Merriman late in camp as he was trying to shift to an end spot in a return from injury.

LB: Lining up behind Buffalo's dangerous line will be a mix of veterans and youngsters at the linebacker spots. Outside starter Nick Barnett (3 sacks, 3 INT) enters his second season with the Bills and led the club with 130 tackles in 2011. Barnett, who spent the first eight seasons of his career with the Green Bay Packers, ranked fourth in the conference in stops. Opposite him will be Arthur Moats (29 tackles, 2.5 sacks), who appeared in 14 games without a start a season ago and is looking to make a home on the outside after beginning his football career as a defensive end before playing both inside and outside linebacker positions with the Bills. Kelvin Sheppard (70 tackles) will enter the season as a starter in the middle in what is his second NFL season. He took over a starting spot by season's end last year and ranked fourth among rookie linebackers in tackles. Bryan Scott (66 tackles, 1 sack, 2 INT) made seven starts as a nickel defender last year and is a primary backup on the outside, as is another veteran in Kirk Morrison. Reserve middle linebacker Scott McKillop hasn't played in the NFL since a stint with San Francisco in 2009 due to an ACL injury, but was productive in college under Wannstedt while the latter was head coach at the University of Pittsburgh.

DB: While the Bills shift to a youth movement at the corner position, they do return the tandem of George Wilson and Jairus Byrd (98 tackles, 3 INT) at the safety positions. Byrd has started 41 games in three seasons -- including all 16 last year -- and had one of Buffalo's four interceptions returned for touchdowns in 2011. Wilson, meanwhile, led the Bills with four picks in 13 games -- missing three with injury -- and ranked fifth among NFL defensive backs with a team-high 106 tackles. Second-year pro Da'Norris Searcy (34 tackles) made three starts in place of Wilson last year and will be the primary backup on the back end. At corner, Drayton Florence, who had three picks and a touchdown, was released to open up a spot for Gilmore. Though there will be a learning curve, the rookie could develop into a playmaker alongside Aaron Williams (32 tackles, 1 INT). Williams was a second-round pick last year who made six starts due to an injury to Terrence McGee, who now shifts to a backup role after having his 2011 season end early due to a torn patellar tendon and restructuring his deal in the offseason. Former first- round pick Leodis McKelvin (39 tackles, 1 INT) will also come off the bench.

SPECIAL TEAMS: The Bills are counting on Rian Lindell to return to form following a shoulder injury that limited him to the first eight games of last season. He hit on 13-of-15 field goals and all 25 of his extra point tries before getting hurt. Lindell has made good on 80.9 percent of his field goal tries over his career. Punter Brian Moorman set a single-season club record with a 48.22 gross punt average last year and pinned 20 of his 72 punts inside the 20-yard line. Justin Rogers took over kick return duties in Week 14 and logged an average of 28.7 yards per runback. McKelvin is set to return punts again and had an 80-yard return for a score last season. Long snapper Garrison Sanborn enters his fourth NFL season.

PROGNOSIS: There is no doubt that the Bills should be considered an up-and- coming team, and their offense will be good enough to win some games on its own. However, the defensive secondary is young at spots and could struggle against veteran quarterbacks on the schedule like Tom Brady, Mark Sanchez and Matt Schaub. Wannstedt is right in saying that it will be the front four that drives the defense, and Buffalo took the right steps through free agency to strengthen the group. Still, the pressure will be on Mario Williams and company. Games against the NFC West as well as the Peyton Manning-less Indianapolis Colts will help, but the Bills will need some wins over the Patriots and Jets, who they went 1-3 against last year while also losing to the Miami Dolphins twice, if they want to be a playoff team.