In a basic defensive formation, there are linemen, linebackers, and defensive backs—three levels. The double-eagle defense is completely different. It features two down linemen in three-point stances—one in the one technique (between the center and guard), the other in the three technique (between the guard and tackle).
After that, there are many possibilities with this defense. The ends are not really defensive ends. They often line up in a two-point stance. In this defense, they're considered a hybrid. You can say the same for the linebackers. The double-eagle version of the ‘Sam' linebacker is called the "rover" linebacker, and often lines up past the outside shoulder of the strongside tight end. Army's rover is senior Steve Erzinger, who is the team's leading tackler.
The cornerbacks line up in different spots as well. Army plays a front cornerback and a back cornerback in their secondary.
Quite simply, the objective of this defense is to cause confusion with different levels.
"The thought process behind it is to put a lot of guys on the line and be aggressive, try to create and cause confusion in the gap, there's also twist games and schemes they run," said Fitzgerald of the double-eagle defense.
On Saturday when the Wildcats' offense takes the field, they will face a tough challenge. Much of that pressure lies on the shoulders of redshirt freshman center Brandon Vitabile.
"It's always on the center, it starts there up front," Fitzgerald said. "But having Ben (Burkett) next to him has helped him already, having a guy who's been there and done it."
The Wildcats' key to success against the defense is simply to control time of possession. This was an area which Northwestern struggled with through the end of 2010, and has been a point of emphasis in the early part of this season. Fitzgerald knows this will likely decide the game on Saturday.
"I can't come in here next Monday and say Army had the ball for over 35 minutes and expect us to be successful," Fitzgerald said. "That just can't happen. If they're over 40 minutes (time of possession), we've got an opportunity for a recipe for disaster. It's a combination of our offense having to move the ball, sustain drives and score touchdowns and our defense has to get off the field and create turnovers."
After months of preparations and film study, Fitzgerald is ready for what will be the Wildcats' toughest tactical test yet.
"It's unique, and their offense is unique," he said. "It makes the whole program step out of what your normal game-planning is and go into a different mode."