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So much of the fanfare surrounding Chip Kelly's inaugural voyage at the helm of the Philadelphia Eagles has centered on his quarterback situation.

That's hardly a surprise considering the position may be the most important in all of sports and Kelly has kicked off his first training camp as mentor of the Birds without a clear plan at the position along with three possible options, descending veteran Michael Vick, second-year man Nick Foles and rookie fourth-round pick Matt Barkley.

It's obviously important for Kelly to establish order at quarterback sooner rather than later but the intrigue over the spot has masked a far bigger issue in South Philadelphia, a defense that looks shakier than cafeteria Jell-O.

First-year defensive coordinator Bill Davis is trying to revamp an entire unit, pivoting away from the old regime's 4-3 mindset and morphing into a hybrid front, whose default setting will be a 3-4 but is far more concerned with disguising the fourth pass-rusher on any given snap.

"I think it gives us a lot more versatility, and I think it causes a lot of problems defensively because you don't know exactly where that fourth rusher is coming from," Kelly said when discussing the change after his first full training camp practice on Friday. "I think there is a versatility in the 3-4 defense that you like, but, again, I think when Billy (Davis) said it, we're going from a wide-9 to a 3-4. When do we get to a 3-4, I don't know. We may have to stop at being a one-gap over and under defense depending upon still making an evaluation of what our guys can do."

The probable change is a hat tip to modern day pro football, which has become a passing-oriented affair with rules heavily-slanted toward the offense. In fact NFL defensive football has become a game of kill or be killed, especially when facing off against elite signal-callers like Aaron Rodgers, Peyton Manning or Tom Brady.

The Eagles' competition in the NFC East -- Washington's Robert Griffin III, New York's Eli Manning and Dallas' Tony Romo -- isn't too shabby either so the prime directive for Davis is get to the quarterback or in the case of a Peyton Manning-type -- a player who simply won't take a sack -- force him to speed up his delivery and get rid of the football quicker than he would like.

The second option is fooling the opposition and that's where the varied fronts and zone-blitz concepts that are en vogue around the league come in.

Door No. 3?

Well, there really isn't a door No. 3 anymore. Playing coverage -- more often than not -- results in death by a 1,000 cuts, so if you fail at the first two objectives, a defense is likely headed off the field with heads held down as the offense celebrates six points.

Davis, who came to Philadelphia after spending the previous two seasons as the linebackers coach in Cleveland, has experience as a coordinator in both Arizona and San Francisco. He faces a mountain of a task with the Eagles and few proven commodities to work with.

Up front, Trent Cole has two Pro Bowls on his resume but is coming off a down year and is now being asked to take on new responsibilities. A prototypical weakside defensive end in a 4-3 scheme, the 30-year old University of Cincinnati product now has to prove he can play in space as a 3-4 rush linebacker.

If Friday's first full-scale workout was any indication, Cole has a long way to go, looking lost in one-on-one coverage drills with the tight ends.

"We're conscious of that," Kelly explained when queried about asking players to do things they are unfamiliar with. "We understand. I don't think it's something that they're going to pick up if they've never been asked to do it. It's like anything. For everybody, no matter who it is, offensively, defensively, it's a whole new offensive system, it's a whole new defensive system, it's a whole new special teams. We're aware of that."

Despite his troubles Cole was actually the standout of the "defensive end" group being asked to do the same thing. Players like Brandon Graham, Phillip Hunt and Everette Brown looked even worse with Hunt, a former CFL pass-rushing star particularly overmatched.

"Trying to find those outside linebackers is kind of the key," Kelly continued. "I think Trent did a nice job today. It's a transition for Trent. It's a transition for Brandon. It's a transition for Phillip. How much they transition. We've still got to play with the roster we have. How far it goes, I don't know. That's really the big question for all of us as we continue to go through the evaluation period.

"We haven't been drafting for this and converting some of those defensive ends to see what they can do. But, our job is to do a great job of figuring out what they do best and then playing to those strengths."

Free agent acquisition Isaac Sopoaga is talked about like a given at nose tackle in Philly but the big Samoan was the weakest link of a talented San Francisco defensive front and will hardly remind you of a Haloti Ngata-type who will command consistent double teams.

"I think we feel better about what we have on the D-line, I think we did a good job of getting guys like (Sopoaga) in here and getting guys like Benny (Logan) in here," Kelly said. We feel like we're a little bit stouter inside than when I first got here in January."

Perhaps, but the back-seven features more question marks.

Remember, the Texans originally gave up on DeMeco Ryans after the 2011 season because the thought in Houston was that the former Alabama star was more of a 4-3 middle 'backer, something Andy Reid bought into and why Ryans was brought to the East Coast. Now Reid is enjoying the barbecue in Kansas City and Ryans is being asked to man the inside of the 3-4 again.

The secondary, meanwhile, could feature four new starters unless the light finally comes on for fourth-year safety Nate Allen. Gone are big-name disappointments Nnamdi Asomugha and Dominique Rodgers-Cromartie at cornerback, replaced by former Ravens Super Bowl starter Cary Williams, who had to leave practice Friday after tweaking his hamstring, and oft-injured ex-Ram Bradley Fletcher.

At safety Allen and the pedestrian Kurt Coleman are trying to hold-off free agent pickups Patrick Chung and Kenny Phillips. Chung is already running with the first-team next to Allen and if Phillips can stay on the field, it's almost a fait accompli that he will beat out Allen.

Of course, even if things break right for the Eagles at all those positions, none of the aforementioned options smell like difference-makers. In fact, Davis' best chance of developing guys who can swing games on Sunday resides in the 2012 draft class (defensive lineman Fletcher Cox and inside linebacker Mychal Kendricks), along with the club's marquee defensive free agent pickup this offseason (former Houston linebacker Connor Barwin).

Cox has the talent to wreak havoc as a five-technique defensive end while Kendricks, although undersized, has the speed and instincts to fly to the football. Barwin, meanwhile, is just a year removed from 11 1/2 sacks and even though pass coverage isn't his forte, he looked like Derrick Brooks compared to some of his 'mates on Friday.

"I think, if you're a good teacher, you don't get frustrated early," Kelly said of the unit's early struggles. "It's a hard transition. We believe it's the best thing for us. The good thing for us is we feel like we've got time. Four preseason games, and you're more than a month away from your first regular season game."