PHILADELPHIA (973espn.com) - The truly elite quarterbacks in the NFL have one thing in common.

They are maestros at the line of scrimmage, extensions of the coaching staff who can run the entire offense from the field, getting their teams out of bad plays and into good ones with an audible or even a hand signal. They can vary their cadence from play and play and often steal five yards in a key spot by drawing an opposing pass rusher offside.

Eagles defensive coordinator Billy Davis spoke about one of those franchise-level QBs on Tuesday at the NovaCare Complex in advance of Philadelphia's upcoming game against the New Orleans Saints.

"I think the common theme for all the top five or 10 quarterbacks, however you want to rate them, is that they have the playbook at the line of scrimmage," Davis admitted. "I think those are the hardest (quarterbacks) to defend.  You show a blitz, they run a screen; you don't show a blitz look, you open the box up to where you split the safeties, and they make their best run play.  They are constantly moving off what your look is.

"If you're not ready, (the quarterback) snaps the ball, set hike; if you are ready on the line, he reads what you're in and changes his play.  So I think (when you’re) facing the Drew Breeses of the world, (it’s an) operation where it really is like having a coordinator at quarterback. They can adjust from what you show.  That is the biggest challenge.  (Brees is) very accurate and highly competitive.  I mean, he knows this offense as well as Sean (Saints Head Coach Sean Payton) does, and they work well together.  It's a challenge."

The Saints defense is not facing the same challenge this week and while it's a stretch to assume Sam Bradford could do all those things Davis gushed about Brees, it's also a moot point because even if he was able, no quarterback is allowed to handle things at the line of scrimmage in a Chip Kelly offense.

At times Kelly has claimed his signal callers can audible and in a literal sense they may have a kill option between two plays, but former Eagles Michael Vick and Matt Barkley are already on record saying they never had the capability save for changing protections and usually center Jason Kelce handles that.

"I think we have options within our plays that are dependent on whether they are going to play a big zone or if they are going to come after you," offensive coordinator Pat Shurmur said last month. "So usually you audible when there's extremes. We have things built in that (Bradford) can take advantage of."

In reality when things are going right in Kelly's offense, the tempo is so fast that the quarterback doesn't have time to change things pre-snap and Bradford has already alluded to the fact he doesn't  have an option to check off even when things are moving at a slower pace.

How does Bradford describe his current gig?

"Listen to the play call. Take what's there," he said earlier this season.

Bradford had the ability to audible in St. Louis and needless to say the true stars at the position like Aaron Rodgers, Tom Brady and Peyton Manning change things routinely.

Now Kelly's own defensive coordinator is on record saying the toughest quarterbacks to defend are the ones given the freedom to escape the ego of the head coach.

The hits just keep on coming.

 -John McMullen covers the Eagles and the NFL for 973ESPN.com. You can reach him at jmcmullen44@gmail.com or on Twitter @JFMcMullen