IF THERE IS one position in sports where the most desired thing is stability, it is quarterback.
If there is one position where the Eagles have seen consistent change during the brief era of Chip Kelly, it has been at quarterback.
Whoever takes the Eagles' first snap on Sept. 14 against the Atlanta Falcons - whether it is Sam Bradford, Mark Sanchez, Tim Tebow or somebody else - he will be the third different quarterback to open the season for the Eagles in Kelly's third season.
When Kelly took over the Eagles in 2013, he inherited Andy Reid holdovers Michael Vick and Nick Foles. Vick won the starting job in a closely contested preseason.
Foles got the job when Vick was hurt and then, off the strength of a Pro Bowl campaign, was the starter for 2014 - until he himself got hurt.
Sanchez started the last eight games of 2014.
Now, with Foles traded to the St. Louis Rams for Bradford, a former No. 1 overall pick coming off consecutive season-ending ACL injuries, the Eagles' quarterback situation is in flux again.
"Whoever's gonna give us our chance to win our opening game against Atlanta is what our decision will be made on," Kelly said when asked during minicamp who was favored to be the Opening Day quarterback.
Conventional wisdom is that you can't win Super Bowls without a stable quarterback, and the Eagles are certainly looking for a franchise quarterback - hence the gamble on Bradford.
Still, Kelly and his offensive schemes have shown a remarkable ability to adapt to quarterbacks.
It's not as if Kelly has done what former Redskins coach Joe Gibbs did, winning three Super Bowls with three different starting quarterbacks, but the skill sets of Vick, Foles and Sanchez are extremely different and Kelly has managed to win 20 games with all of them in his first two seasons.
Considering the turnover Kelly ushered in with his new player-personnel control, there will be a lot of things to watch when camp opens on Sunday.
No competition will be more scrutinized than Bradford and Sanchez for the starting spot.
How it plays out could have long-term implications for Kelly's program.
The ideal scenario would be for Bradford to come into training camp fully healthy, clearly win the starting job and then show he has the capabilities to be the franchise quarterback.
Still, there is a reason the Eagles have not renegotiated a long-term contract with Bradford. Actually, there are two reasons, as in two tears of the same ACL in consecutive seasons.
Kelly took a big enough gamble by trading Foles and a second-round draft pick for Bradford. If it goes wrong, it would only exacerbate the mistake by having Bradford locked into a long-term deal.
If Bradford does prove his worth, then the Birds will just have to pony up at the end of the season and pay him the going rate for a potential Super Bowl-winning quarterback.
That, however, was something eventually they were always going to have to do whether they had stuck with Foles, traded up to draft Marcus Mariota or found someone else to be the franchise quarterback.
We won't know if Bradford is healthy enough to start training camp until he gets there.
If he isn't, and then misses more than a few practices, Sanchez could take the No. 1 position and run away with it.
A lot of fans may not have confidence in Sanchez, but he is the quarterback the Eagles gave a two-year contract worth $16 million ($5.5 million of which is guaranteed).
Sanchez started the final eight games last season and went 4-4, so he already has a considerable advantage of actual NFL game experience in Kelly's system.
Another year removed from the torn labrum shoulder that cost him the 2013 season, Sanchez said during minicamp, "First thing, physically I feel so much better. The farther it gets away from surgery and all the reps I've had, all the rehab on through, it only can get better and better and stronger."
Sanchez will come in to training camp with the mindset that the starting job is his to lose. He won't meekly surrender it.
What will be interesting to see is what Kelly would do if Bradford is not ready to play until a few games into the regular season, while Sanchez has looked good and has the Eagles at 3-1.
Would Kelly dare make a quarterback change?
He is a risk taker, but his action in 2013 when Foles took over for an injured Vick and then played lights out indicates Kelly would not.
Few people would consider it a real option, but what if Sanchez is the one who plays his way into the role of franchise quarterback?
Sanchez (28) was born on Nov. 11, 1986. Bradford was born on Nov. 8, 1987. Neither is deemed to have fully realized his potential as an NFL quarterback.
Just as the hope is that Bradford will regain the form that made him the No. 1 overall pick in the 2010 NFL Draft, there is a chance that Sanchez still has time to live up to being the fifth overall selection in 2009.
Kelly is just looking to find a quarterback with whom to move forward. He'll let the candidates determine who that will be.
"When you get to have the same quarterback play in the same system," Kelly said, "I just think it's beneficial.
"That's what you hope when you get a quarterback you can hang your hat on, who's going to be here for awhile. We'd like to get a quarterback in here that we can build the rest of the team around."