There's the 4-3 defense. The 3-4 defense. And the mystery defense.
The latter belongs to the Washington Redskins. Hey, it may turn out to be two taste treats in one.
How and who the Redskins line up in 2010 are critical questions going forward for coach Mike Shanahan. His defensive coordinator, Jim Haslett, played in the 3-4 and he has preferred it as a coach.
The Redskins historically clung to a 4-3 alignment -- four defensive lineman and three linebackers. When free agency kicks off on Friday, players the Redskins pursue may give a clearer picture than Shanahan has so far.
His comments so far indicate a hybrid scheme. As, in many ways, most defenses are. A base 3-4 (that's three linemen and four linebackers) gives way to numerous sub packages as the situation dictates and a player like Brian Orakpo, who plays both end and linebacker, lend that flexibility.
Everything seems to go in cycles in the NFL and the 3-4 is once again the rage. The Kansas City Chiefs, Denver Broncos and Green Bay Packers made the move a year ago and the Buffalo Bills will do it this season.
It's a style, not a lifetime commitment.
The Dallas Cowboys rose to prominence with their 4-3 "Flex" but they're a 3-4 team today. The New York Giants won two Super Bowls under Bill Parcells as a 3-4 team but they're a 4-3 club. The Bills played the 3-4 when they went to four consecutive Super Bowls in the 1990s. Times change.
The success of the New England Patriots since 2001 and the dispersal through the league of their front-office people and former assistant coaches helped spread the 3-4 gospel. When Scott Pioli took over in Kansas City, the defense changed. When Josh McDaniels moved to Denver, the Broncos altered their approach. Eric Mangini's exit from New England for the New York Jets in 2006 brought the 3-4 to the Meadowlands.
"It looks like half the league is employing some 3-4 type of configuration," says Nick Caserio, the Patriots director of player personnel.
Close enough estimate. Looks like 15 of the 32, including the Redskins. Every team in the AFC East goes 3-4 with Buffalo joining the party. Three out of four in the AFC North do it, with the Cincinnati Bengals the lone holdout.
How tough is the transition?
"I guess that depends on (if) you are changing coverages or is it just the front?" says Jets coach Rex Ryan. "There are several different versions of a 3-4. But it depends on your style. If the coverages are staying the same, it probably is not as big a change as what you might think."
The proliferation of the 3-4 has raised the profile of the nose tackle, the anchor of the front. The 3-4 commands fewer adherents in the college ranks so the prototypical NFL nose tackle sometimes must be created or molded. NFL teams jealously guarded their prizes last week when they named their franchise players, those key people now almost completely exempted from the market forces of free agency.
Six teams used the franchise tag, three of them tagging their nose men. The Patriots started the action by putting the tag on Vince Wilfork. Green Bay designated Ryan Pickett and the San Francisco 49ers tagged Aubrayo Franklin. The Pittsburgh Steelers, the godfathers of the 3-4, reached a contract agreement with Casey Hampton with the franchise tag a ready tool in their kit.
"Defensive linemen in general are tough to find, especially for 3-4 defenses," says Kevin Colbert, the Steelers director of football operations.
So there's the question for the Redskins as they consider the 3-4. Who plays the nose? Who sits in the middle? And how does he play? Not every 3-4 asks the nose tackle to line up head-on against the center and eat up two blockers. Some, like Dallas', employ a quick penetrator.
Perhaps the Redskins can ask Phillip Daniels to take on that role. He has played inside and outside in his 13-year career and possesses the strength to "two-gap," or cover the areas to the right and left of the center.
Albert Haynesworth combines strength and agility but prefers to be an up-the-field player rather than one who holds the point of attack. Then again, maybe that nose tackle is not yet on the roster.
Haslett told Haynesworth not to worry what position he will play, that he could be lined up on the nose, at end or even linebacker. Whatever works best for the player and the team.
"He'd be scary if he was on the center or a weak guard," Haslett says.
Scary? Scary is good.
The 4-3? The 3-4? A little bit of both? That's all part of the mystery of how the Redskins will line up. And who.