When Nick Foles is good, he's really, really good.

This streakiness has shown up most notably in his deep attempts. Against Tampa Bay and Oakland, he threw 10 passes longer than 20 yards, completing eight of them for 295 yards and six touchdowns. Sandwiched between those efforts was the ugly game against Dallas, in which his longest gain all day netted just 14 yards.

When he's been on, Foles' numbers have been equally absurd in the screen game, which thanks to Chip Kelly now comprises a dizzying array of short throws attacking every area of the field. That New England offensive coordinator Charlie Weis called back-to-back screens in Super Bowl XXXIX was later seen by some as proof positive the Patriots really had stolen the Eagles' defensive signals, because why else would there be such madness?

Well, against Tampa Bay, the Eagles ran a zero-yard hitch route and three screens in a row (running back, tight end, wide receiver) as they marched down the field during the second quarter.

These plays haven't been going for little chunks, either. Last year, the stats wizards at Football Outsiders tracked just under 3,000 passes that didn't cross the line of scrimmage. Quarterbacks completed 75 percent of these attempts, with the average result for all these plays being a gain of just under five yards (six-and-a-half yards per completion).

Against Tampa Bay and Oakland, Foles attempted 19 such passes, completing 18 of them for 202 yards –or more than 10 yards per attempt. That's averaging a first down on passes that don't even cross the imaginary black line.

Part of the reason they had this success against Oakland was how much room the Raiders' defensive backs gave the wide receivers:

In that second shot, DeSean already has the ball and is turning up field.

It's a similar setup on Cooper's big catch and run:

Not only do the Eagles have a "hat on a hat" outside, the second defender is 20 years away and in no position to limit this to a short gain.

This spacing issue especially matters because of a quirk in the rulebook. In the college game, if the pass is thrown behind the line of scrimmage, eligible receivers can legally block downfield while the ball is in the air. In the NFL, it doesn't matter where the pass is thrown – if the ball's in the air and you're blocking downfield, that's offensive pass interference, as we saw in the preseason with this play where Avant got flagged:

The Eagles are much less obliging in their pre-snap defensive positioning, as we can see in these two very similar setups from last Sunday:

In fact, one of the stories of the day was the way the Eagles' defense looked completely prepared to face the challenge of a "college" offense run by a mobile quarterback.

Terrelle Pryor certainly helped the Eagles' cause with his mistakes. Somehow he couldn't find a single open receiver on this red zone play:

And on the Trent Cole sack – which I timed at over five seconds from snap to trip – Pryor only had eyes for the double-covered receiver running down the sideline, missing a friendly face wide open in the middle of the field:

But Pryor is a dual-threat quarterback and was coming off a win over Pittsburgh where he'd run for more yards than he'd managed through the air. So they had to plan for that part of his game as well.

One difference between the Chip Kelly offense and what Pryor is running this year is the direction of the read on the option. As most Eagles fans know by now, Kelly's scheme leaves a defender unblocked on the back side of the play. In contrast:

Pryor is (generally) reading a defender on the front side of the play. The principles are otherwise the same. If the edge defender – Barwin in the picture above – attacks the running back, the quarterback keeps the ball and vice versa.

From the game's first snap, the Eagles' plan was clear. They were going to send Barwin and Cole screaming down the line to stack up the running back, force Pryor to keep the ball, and leave it up to the linebackers and safeties to bring him down. Continuing the play from above, Barwin goes so far as to tackle the non-ball-carrier inside while Pryor escapes outside, where Mychal Kendricks and Co. will chase him down after a short gain:

This leads into a topic I've wanted to cover all season, but haven't been able to squeeze into one of these game reviews. We know Chip Kelly wants to run a two-gap, 3-4 defense, even though the Eagles don't really have all the pieces needed for it. The question that hasn't really been asked is "Why?"

Every week, my fellow members of the screenshot guild diagram plays in which Kelly uses simple math to put the defense in impossible situations. That's the genius of the spread offense. You need seven men inside to stop the run and four outside to stop the pass, so unless you want to play the whole game without even one safety, you have to leave something open. Defenses just can't cover everything.

Unless … the defense can do this:

This is somewhat similar to the Eagles' outside zone play. And with six blockers facing six defenders, the Raiders should be able to run the ball here.

The catch is that on the snap Fletcher Cox and Cedric Thornton are each able to occupy two blockers inside. Without those guards being able to climb to the linebackers, the numbers are no longer there for the offense. Pryor's going to keep the ball here and run outside, but an unblocked DeMeco Ryans is tracking him all the way:

I'm convinced this is the reason for Chip's stubbornness about his scheme. If the spread offense really is the future of NFL football, he wants a defense that can stop it.

Eagles fans hope he's right on all counts.

Derek Sarley can be reached @igglesblog. His work can also be seen at www.igglesblog.com.