Five things you need to know about the Eagles:

1. Chip Kelly will make a splash: There is more national interest in Kelly than the other seven new head coaches combined. Mike McCoy? Marc Trestman? Everyone wants to see what the Oregon guru can do at the NFL level. That cuts both ways: Veteran NFL defensive coaches will compete to solve the riddles posed by Kelly's fast-break offense. Kelly will throw the first punch on Sept. 9, when he unveils his system on "Monday Night Football." The counterpunching will begin the moment opponents have film to work with.

2. Michael Vick gets one more last chance: Everyone knows the numbers. Vick has missed nine of 32 starts the past two years. When he has been on the field, he has turned the ball over 32 times (24 interceptions, eight fumbles lost) in 23 games. The difference this year, of course, is Kelly's quick-paced system. If Vick can get the ball out quickly, avoid big hits and stay healthy, he'll have a chance for a late-career renaissance.

3. The O-line is healthy: This could go a long way toward keeping Vick upright and in the starting lineup. Vick was sacked 28 times in just 10 games last year. Although he will run the ball by design in this offense, Vick has sustained the most physical damage being hit in the pocket. Last year, with LT Jason Peters out all season and injuries to C Jason Kelce and RG Todd Herremans, the line was a mess. This year, with first-round pick Lane Johnson (RT) joining the healthy core group, it could be among the best units in the league.

4. 3-4, 4-3 or somewhere in between: Kelly is all about innovation on offense. He is leaving the defensive side of the ball to new coordinator Bill Davis, who is attempting to switch from a 4-3 front to a variation of the 3-4. Davis will be trying to adjust his defense around his players all through the season. The changes should challenge veteran Trent Cole, who moves from DE to OLB, and should provide opportunities for DE Fletcher Cox and ILB Mychal Kendricks to establish themselves. Connor Barwin, the OLB signed from Houston, could have a breakout season.

5. The secondary is primary: The Eagles will have three or four new starters in their defensive backfield. That depends on Nate Allen's ability to hang on to the strong safety spot. There's a reason. The secondary was brutal in 2012, allowing a league-high 33 touchdown passes. GM Howie Roseman cleaned house, bringing in four new veteran DBs and parting ways with former Pro Bowl CBs Nnamdi Asomugha and Dominique Rodgers-Cromartie. Davis has to find at least six players he can count on.

-- Phil Sheridan, ESPN.com

New head coach Chip Kelly may be changing the way the Eagles play on offense, but if Philadelphia wants to return to the postseason, it's the defense that will need the biggest changes.

The Eagles' pass defense fell apart after the firing of defensive coordinator Juan Castillo last season. Before his firing during the Week 7 bye week, the Eagles had the third-best opponent Total QBR (28.2) and had just as many interceptions as touchdown passes allowed (seven).

After Castillo was fired, the Eagles allowed a league-worst 79.4 Total QBR and 26 touchdown passes to just one interception.

The unit's biggest struggle was on deep throws. In the last 10 games of the season, the Eagles allowed opponents to complete 59.4 percent of their attempts thrown more than 20 yards downfield, well above the league average of 33.8 percent. During that same stretch, no other team allowed opponents to complete 45.5 percent of those throws.

" The Eagles' offensive line allowed their quarterbacks to get sacked or put under duress on 29.5 percent of drop-backs last season, the second-worst rate in the NFL. In addition, Eagles running backs were contacted in the backfield on 21.5 percent of their rushes, also the second-worst rate in the league.

• LeSean McCoy had one rushing touchdown in between the tackles last season after scoring 10 such touchdowns in 2011 (T-2 in the NFL).

-- ESPN Stats & Information