In the last two games, the Eagles offense has scored just three points in 25 possessions. That shouldn't be easy to do, particularly for an offense that averaged 28 points and 450 yards in the first six games of the season. The Eagles made it look easy, though, in their flat efforts against the Cowboys and the Giants.

Chip Kelly, brought to town as an offensive genius, is aware of all this. He is asked if opposing teams have figured out his scheme. He is asked if the talent is good enough to get the job done. He is asked if some of his nifty plays shouldn't be replaced by more fundamental football calls.

These are not questions he was asked before, of course, but he did have an answer ready.

"We were successful for six games," Kelly said. "The last two, if I look at the last two and just analyze what the situation is, in both games we got to our third quarterback. I think that's a difficult proposition."

Not a bad point. At the moment, the Eagles are still fifth in the league in net yards per game, behind Denver, Green Bay, Detroit, and San Diego. How would those teams do in a given week with Zac Dysert, Scott Tolzien, Kellen Moore, and Brad Sorensen at quarterback instead of Peyton Manning, Aaron Rodgers, Matt Stafford, and Philip Rivers?

Kelly wasn't blaming Matt Barkley, who was on the field for only 11 of those 25 possessions, by the way. He was just saying the same thing every NFL coach would say in the same situation. If the offense worked before and then it stopped, what was different? In this case, the most obvious answer is the quarterback situation.

Whatever part of the blame Kelly shares for last Sunday's loss to the Giants, in which Michael Vick not surprisingly reinjured his hamstring and an unprepared Barkley entered the game, some of that is the nature of the NFL, too. After sitting out for two weeks, Vick needed all the practice reps he could get. Every coach would have made the same choice, according to Kelly.

"That's how it's sliced," Kelly said.

He sliced it the same way in practice leading up to Sunday's game in Oakland. Nick Foles, returning from a concussion after missing a full week of work, needed all the reps he could get, and he got them. If Foles is knocked out of the Raiders game, Barkley will come in just as unprepared.

This may not sit well with the fans, but the Eagles reached the midway mark of the season with a 3-5 record, and that's probably about where they should be based on the injuries. More troubling than the vagaries of this year's bad luck is the long-term question of whether Kelly's methods will invite such luck every season.

This time around, it's no shock that Vick broke down or that Foles froze in the headlights of his own bad game and got clobbered. In the future, however, after Kelly finds his real quarterback - someone like Marcus Mariota from Oregon - will keeping him on the field in a system that requires quarterback risk be a constant challenge?

Well, maybe. As with the quarterbacks, Kelly is merely playing the hand he holds this season. That includes the fact that only two skill-position players, DeSean Jackson and LeSean McCoy, require particular attention from the opposition. A defense can assign single coverage to Riley Cooper, Jason Avant, and the tight end, and essentially double-team both Jackson and McCoy. Stuff the run; force the pass; and, at least since Vick went out, don't worry about the quarterback as a running threat.

In Kelly's vision of the offense, that isn't usually the case. The quarterback doesn't have to run, but he has to be able to run well enough that defenses must account for him. If the option rushes are going to work, the defense has to split its attention between the quarterback and the running back, unlike the suffocating situation McCoy faces right now.

Boil down everything else and that is what remains, which is why it doesn't really matter whether Foles has a bounce-back game against the Raiders or whether Vick eventually returns along with his diminishing mobility. It is interesting enough to follow, but this season is for learning, and Kelly is learning that his quarterback must be able to run better than any of the three he has now.

What he has also learned is that backup quarterbacks lose, although that wasn't much of a revelation. What is still to be learned, however, is whether a true Chip Kelly quarterback will be able to stay on the field in the NFL, or whether the punishment required will often leave the team with a backup who didn't get any meaningful practice the previous week.

That might be how it is sliced, and somewhere down the line we'll see if the blade of his offense really cuts two ways.