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UNC's previous pro-style defense reflected the long-held beliefs of its head coach. Butch Davis played defensive end at Arkansas and later coached the defensive line at Miami and Dallas. That background effectively provided the groundwork for a Tar Heel defense designed to wreak havoc at the line of scrimmage while the back seven operated out of a zone -- otherwise known as a Cover 2 -- that split the field in half.
When the defensive line was able to apply pressure and collapse the pocket, the back seven reaped the benefits with 72 interceptions over the past four seasons. That zone approach, however, failed when opposing offensive lines bought their quarterbacks enough time to find holes – UNC ranked 78th nationally in pass defense (241.3 ypg) in 2011.
Under the previous regime, UNC's defensive linemen had varying responsibilities. One end and one three-technique tackle were given specific gap assignments, while the other two linemen could rush from whatever angle they deemed most effective.
Defensive tackle Sylvester Williams described that approach as "more freestyle" than anything else. The New York Giants proved that method could work with their 2007 Super Bowl win over heavily-favored New England – a game that Davis often referred to while talking defense – but three-step drops and spread offenses at the college level could neutralize that strategy.
Enter Larry Fedora's 4-2-5 aggressive defensive scheme. In order to blitz as often as co-defensive coordinators Vic Koenning and Dan Disch would like, free-styling at the line of scrimmage is out of the question.
"It's a defense where you actually have to do your job," Williams said. "You can't get out of control because every gap is accounted for. When I say accounted for, I don't mean that it's a linebacker sitting seven yards back. I mean it's literally a linebacker hitting that gap.
"So for me to say to myself, ‘I'm going to be selfish and get out of my gap,' I'll be hurting my team because there would be two people in one gap and I'd be cutting off a blitzer. You have to be disciplined in this defense."
That realization is eight months in the making. During spring ball, UNC's defensive linemen instinctually attacked the open gaps along the line of scrimmage, not making the connection that the play call set up those gaps to be hit by one of the back seven.
The sheer volume of blitz calls has made the entire defensive line become more "gap conscious," according to junior defensive end Kareem Martin.
"Even though the gap may be open, if you try to go in there, you may be cutting off a blitzing linebacker or a Bandit who is looping back in," Martin said.
By limiting the defense's individual options – two-way go's are essentially relics now – the coaching staff has removed overthinking from the equation. With only one assignment on any given play, whether its attack or cover, the players can play fast and loose.
"The coaching staff brought us all together for a meeting and told us that once you learn [the defense], you can really just be free, have fun, fly around and be physical," cornerback Tim Scott said.
For Martin, the key was learning his teammates' responsibilities – something that hadn't been much of a concern during his first two seasons at UNC.
"It was difficult at first when I didn't know where everybody needed to be, but now that I have a feel for the defense as a whole, I can play fast and I know when I can go inside or when I have a back-up blitzer," Martin said. "I feel more comfortable and I can play in an attacking way but under control at the same time."
Disch and Koenning both ran similar versions of the 4-2-5 last season – at Southern Miss and Illinois, respectively – and combined to force 50 turnovers.
North Carolina's 4-2-5 will finally be revealed against Elon on Saturday. It's difficult to ascertain an educated guess as to what the scheme will ultimately hold, but it's worth noting that Fedora has been pleased with his defense's work during camp.
"I thought they really started out camp pretty strong," Fedora said on Wednesday. "They were way ahead of where we were offensively. Because of the things that we do defensively, it gives you problems offensively. I think they've progressed right along. The key is they've done a good job of getting a lot of guys some reps so that we can count on some other guys because you know more than 11 are going to have to play."
There's also a good chance that 11 or more players will register sacks in 2012. Eleven Southern Miss defenders notched sacks last fall, while 13 Illini players were credited with sacking a quarterback.