Buffalo Bills head coach Doug Marrone has reportedly hired Mike Pettine, formerly of the New York Jets, as his new defensive coordinator. That move has not yet been made official; even when it is, we may not have a good idea as to whether the Rex Ryan 3-4 disciple plans to stick with that scheme or operate out of a base 4-3 in his new job.
In either case, NFL teams spend so much time in sub packages to account for pass-heavy, spread-happy offenses that the importance of a base defense is significantly lower than what it used to be. The Bills, for instance, were roughly split 55-45 in favor of their nickel and dime packages (which featured linebacker Bryan Scott, who played 54.2 percent of snaps) over their base 4-3 (which featured linebacker Kelvin Sheppard, who played 46.3 percent of snaps). The Jets, too, dabbled more with the 4-3 last season than in years past thanks to division rivals New England and Buffalo and their receiver-laden play sheets.
While it's not as big a deal as it used to be, however, which base defense is in use is still a very important decision, and one that will shape how the team attempts to improve the roster this off-season. The Bills were built to run a 4-3; if Pettine switches them to a 3-4 - even if it's only for 40 percent of snaps - X big questions will arise.
Where will Mario Williams play?
Obviously, in essentially every nickel and dime package, Williams will have his hand in the dirt rushing the passer as he normally does. There has been some talk that Mario could see work as a 3-4 defensive end under Pettine; he certainly has the physical measurements to pull that off, but he's not an especially powerful player at the point of attack, and is a better boundary run defender thanks to his size and range. That end role may be used situationally, but far more likely than not, Williams would be asked to be a pass-rushing outside linebacker in a 3-4 base.
Who else rushes the passer?
Mark Anderson, who only appeared in five games and recorded one sack before a knee injury that required two surgeries, is still under contract. He is not a snug fit for the 3-4 outside linebacker role, however, much like Williams, who represents a significantly larger investment. Chris Kelsay, who has looked miserable in this role before, is also coming off of a neck injury, and it would not be terribly surprising if the 33-year-old was released or retired. Kyle Moore is a free agent, and is purely a 4-3 end type. Shawne Merriman is also a free agent, and is a shell of his former self. Buffalo would need to find a complement to Williams at outside linebacker - particularly if Pettine is iffy on Anderson, and especially one that can add an explosive element to the pass rush.
Where's the beef?
Specifically, where's the nose tackle? The team has three prospects for that position: Kyle Williams, Marcell Dareus and Torell Troup. Williams is a one-gap player that thrives on being the first player off the ball; he is not a space-eating run stuffer. Dareus has the physical measurements to play that role, but his style is more reminiscent of Williams'. Troup, the player originally drafted by this team to be that interior space-eater back in 2010, is coming off of serious back surgery and is no lock to make the team next season. Buffalo may need a player capable of filling that two-gap nose guard role so that Pettine can put Williams and Dareus in better position to do what they do best: get into the backfield.
Other questions - like whether or not key free agents (chiefly Jairus Byrd) will be retained, or whether or not the team needs better linebackers, among others - remain largely the same regardless of scheme.