Although much of the focus Sunday will rightfully be on the Patriots defense against the Bills offense, the biggest change in this rivalry has come on the defensive side of the ball for Buffalo.

Dave Wannstedt, after an eight-year absence following his dismissal as Dolphins coach during the 2004 season, is back directing an AFC East defense as coordinator for the Bills (2-1).

Wannstedt has tinkered a bit with his 4-3 scheme, but it essentially has remained the same and is unique to the NFL. He puts a lot of pressure on his line, middle linebacker, and cornerbacks, and those players must be supremely talented for it to work.

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Wannstedt seldom likes to blitz, though he is doing that more this time around with linebacker rushes. The cornerbacks are asked to play press coverage a majority of the time, with safety help over the top. And the tackles have to take up blockers to keep the linemen off the linebackers, who are asked to clean up against the run.

Patriots quarterback Tom Brady has had mixed results against Wannstedt in his career, though considering how much the game has changed, it’s almost impossible to compare statistics from eight years ago with today.

Brady was 5-3 against Wannstedt’s Dolphins. He completed 130 of 231 passes (56.3 percent) for 1,348 yards (5.8 yards per attempt) with 11 touchdowns and 8 interceptions. His quarterback rating was 74.7. Brady has completed more than 62 percent of his passes only once against a Wannstedt defense, and has never thrown for more than 283 yards.

A look at the Bills:

DEFENSE

General manager Buddy Nix gave Wannstedt some very nice tools with a front line of ends Mario Williams (1.5 sacks), former Patriot Mark Anderson (one sack), Chris Kelsay, and Alex Carrington (one sack as interior sub rusher). Williams (left end) and Anderson (right end) have not had instant impacts as free agents. Anderson has lost snaps to Kelsay, who is very good against the run. The Bills will run a lot of stunts and twists up front against the pass . . . Nick Barnett has moved from the middle to weak-side linebacker and leads the team with 23 tackles. Arthur Moats (strong) and Kelvin Sheppard (middle) have been solid. Bryan Scott will help the linebackers in pass coverage and is very good and physical . . . First-round pick Stephon Gilmore is still feeling his way at right cornerback. Aaron Williams is the left corner. Justin Rogers is the nickel, and Leodis McKelvin will come in at linebacker in the dime package . . . Safeties Jairus Byrd and George Wilson are ballhawks.

OFFENSE

Coach Chan Gailey runs a spread-influenced offense with motion, pistol formations, and play fakes. Buffalo loves to spread the defense out with multiple receivers and will throw bunch formations and rub routes to put stress on the defensive backs . . . Former Harvard quarterback Ryan Fitzpatrick has gotten off to a solid start (58.1 completion percentage, eight touchdowns, three interceptions), but he’s still wildly inconsistent despite the arrival of former Dolphins quarterbacks coach David Lee. Fitzpatrick’s fundamentals are still poor and his woes only increase with stress. He will throw passes into bad spots if pressed . . . Receiver Stevie Johnson is one of the league’s best against man coverage. He has touchdowns in his last four games. Donald Jones, rookie T.J. Graham, and tight end Scott Chandler are all capable . . . The Bills will likely get running back Fred Jackson (LCL sprain) back, while C.J. Spiller, who leads the league with 422 scrimmage yards, will likely be out with a shoulder sprain. Tashard Choice has been a capable fill-in, and will run with the Wildcat, along with receiver Brad Smith . . . Cordy Glenn, a second-round pick, has done a surprisingly solid job at left tackle. Left guard Andy Levitre has had some struggles, while center Eric Wood and right guard Kraig Urbik are good. Very good right tackle Erik Pears has had increased playing time after dealing with a groin injury in the preseason.

SPECIAL TEAMS

McKelvin already has a punt return for a touchdown this season, and had a 33-yard return against the Browns Sunday. He is extremely dangerous returning punts and kickoffs . . . The Bills made the curious choice to cut veteran Pro Bowl punter Brian Moorman this week for rookie Shawn Powell. Moorman had some very poor directional kicks against dangerous Browns returner Joshua Cribbs. The Moorman release could have a big effect on kicker Rian Lindell because Moorman has been the long-time holder . . . Scott and Delano Howell are top special teams players.