The Dallas Cowboys' offense has struggled since the early parts of the season, and that was something many expected after the first two games. After losing running back DeMarco Murray in the offseason, wide receiver Dez Bryant in Week 1 and quarterback Tony Romo in Week 2, it's been tough for them to sustain offense through the air. While the ground game still ranks in the top 10 in the NFL, the Cowboys have cycled in Brandon Weeden as well as Matt Cassel at quarterback for the injured Romo.

What made matters worse for them up until last week was that, with Bryant on the sidelines, teams were able to make more of a concerted effort to remove tight end Jason Witten from the progression with different uses of double coverage schemes. I explained this a couple of weeks ago after the Eagles’ win over New York, but true double coverage in the NFL isn't as common as you may think? Defenses have to pick their spots when they assign two defenders to cover one receiver, and it puts additional stress on everyone involved.

Defenders responsible for the remaining four eligible receivers have less help over the middle or in the deep part of the field, the defensive coordinator is more limited with what he can do from a blitzing standpoint and there are still gap assignments that defenders must be responsible for in the run game. The Eagles have shown in the past that they are willing to assign two defenders to a receiver in certain situations, they've done it with both Witten and Bryant. They did it a couple of weeks ago against Giants receiver Odell Beckham Jr., but what does that mean for the rest of the defense?

First, it comes down to pressure.

It's Week 4 against New Orleans. On this third-and-9 play, the Cowboys have Witten run an over route across the field.

The Saints take Witten away with a cornerback and a linebacker in the middle of the field. This is important because these are the types of situations where you typically see double coverage tactics like this one - in the red zone and on third down. The Saints have man coverage across the board with one safety in the middle of the field and just a basic four-man rush. Again, you can't blitz the quarterback AND double cover a top threat AND give help to everyone else across the formation. You have to spend your resources wisely. What happens on this play?

Shot 1 - Bracket Coverage vs Witten by the #Saints. Have to rely on 4-man rush to get home. pic.twitter.com/YfkuSiDsqi — Fran Duffy (@fduffy3) November 4, 2015

Rookie Hau'oli Kikaha beats Tyron Smith around the corner, beats a cut block and brings Weeden down for the sack.

Here's another play from a week later against New England. It's third down, and again Witten is coming across the formation on an over route with Cole Beasley at the top of the screen running a quick pivot route to the outside.

The ball is snapped, Weeden drops back and right away you can see Rob Ninkovich team up with the cornerback at the top of the screen take Beasley away. Ninkovich has his eyes outside, so he can take away any in-breaking route and any out-breaking route can go to the corner. At the bottom, New England dropped Chandler Jones and he has his eyes on Witten immediately in his drop, so he provides help to the cornerback to take him away.

Weeden's eyes are locked up. Both of his primary targets have been taken away, and a four-man rush gets home when Donta Hightower defeats the block from Darren McFadden and gets the sack.

Again, the Eagles have executed plays like this as well, and we saw it on Monday Night Football against the Giants.

It's second-and-10, and the Eagles have two sets of eyes on Odell Beckham Jr., with Nolan Carroll playing underneath in man coverage and Walter Thurmond helping to take any vertical routes away over the top. The Eagles have a single-high safety in the middle of the field, man coverage across the rest of the field and just a four-man rush.

The rush gets home, as Brandon Graham and Connor Barwin collapse the pocket to sack Eli Manning.

What's the point I'm trying to make here? If and when the Eagles double-cover anyone on the Cowboys' offense, whether it's Dez Bryant or Jason Witten or anyone else, they will need the rush to get home to prevent the quarterback from getting through the rest of his progressions to deliver the football.

The other area of focus when it comes to double coverage is the other one-on-one matchups that it creates across the rest of the formation.

Down in the red zone against New Orleans, the Cowboys ask Witten to run an over route across the field. Notice a trend starting here?

This is another form of double coverage, a "bracket" from the Saints with both safeties' eyes on Witten as he enters the secondary. This creates a one-on-one with Williams on the outside, but he's unable to win the matchup and the pass falls incomplete. Situations like these have been an issue for the Cowboys throughout the course of the season.

The following week against New England, Witten is doubled in the middle of the field by a corner and a linebacker. Devin Street is running a slant route on this "slant-flat" combination on the outside.

Street actually wins on this route, gaining separation and breaking open for Weeden, but he's unable to complete the catch on third down and the Cowboys are forced to punt. Winning the one-on-one matchups with Dez Bryant out of the lineup has been an issue for the Dallas receiving corps.

What does this mean for the Eagles' defense? It means that the defenders responsible for covering these receivers in one-on-one situations have to remain sound in their technique throughout the down.

This is a shot from Week 15 from last year against Dallas. On third down in the red zone (those two situations coming up again), the Eagles call for double coverage on Witten and Bryant. The receiver is running a vertical route from the slot, and is covered by safety Nate Allen (this will be Thurmond now) and Bradley Fletcher (insert Byron Maxwell). On the outside at the top of the screen, Witten is also running vertical, with Nolan Carroll and Malcolm Jenkins responsible for him. This creates three one-on-one matchups across the board for the Eagles' defense, and a four-man rush. Brandon Boykin was matched up on Beasley, Mychal Kendricks had Murray out of the backfield and Cary Williams was responsible for Williams at the bottom of the screen.

As you can see, the double coverage works to perfection. But Cary Williams allows Terrance Williams to beat him inside, where he has no help, and he makes the catch for the first down. It will be imperative for the Eagles' secondary to not let this happen on Sunday night, and if you want to feel confident, you just have to look back at the matchup against New York.

It's first-and-10, and with Beckham in the slot. Malcolm Jenkins lines up across from him, and at the snap of the ball he will play with outside leverage, forcing Beckham to go inside toward his help. Thurmond, playing on the near hash, has his eyes on Beckham from the jump, and is available to help Jenkins in coverage. Safety Chris Maragos will play as the single-high safety in the middle of the field. Eli Manning tries to hit this Go route over the top down the left sideline. That's a long way for Maragos to travel, so if his receiver can beat Carroll off the line, this should be a big play for the Giants.

Carroll plays this about as well as he can play a vertical route, staying hip-to-hip with the receiver, pinning him to the sideline and then looking to find the ball. Ideally, he comes away with the interception there, but the result is an incomplete pass to bring up second-and-long. If the Eagles' secondary can trust its technique and play to the level that they practice week in and week out, they'll be able to win more of these one-on-one matchups than they lose on the outside.

Enough about the Dallas passing game, because we all know that this offense wants to run the football, and they do it well. Despite the fact that Murray now calls Philadelphia home, the Cowboys still average nearly 130 yards per game on the ground, good for sixth in the NFL, and that's in large part because of that offensive line. We all know Tyron Smith is one of the best tackles in the NFL, and Travis Frederick has quickly turned into one of the top centers in the league as well. Last year's first-round pick, Zack Martin, was an All-Pro in his first year in the league. Now when you add rookie free agent La'El Collins (who grew up a Cowboys fan, so it's no surprise he ended up there after not hearing his name called due to potential off-field concerns in April) to the mix, you have a very tough offensive line to deal with.

This is a simple sweep play from the Cowboys, one of their staple plays in the run game, and look at Collins (who played tackle his senior season at LSU) get out on the move and vault not only Bobby Wagner, but toss Earl Thomas aside like a rag doll out in space.

Here's a play from the same game, this time on their favorite run play, the outside zone stretch. Look at what Collins does to Brandon Mebane, one of the best nose tackles in the league at the end of this play, as he nearly bench presses him out of the frame. Collins is athletic. He's powerful, and he plays with a nasty streak to him that allows him to fit right in on this offensive line.

Since Dallas likes to run the ball, you'll often see them come out in heavier packages. The Cowboys play a good amount of snaps in 12 personnel (one back, two tight ends), 13 personnel (one back, three tight ends) and 23 personnel (two backs, three tight ends). When they break the huddle in those sets, you'll typically see heavy run-first formations like this one.

The Cowboys line up in 13 personnel on this play against the Giants, with just one receiver split out wide, one running back and three eligible tight ends all lined up along the line of scrimmage.

While this is considered a "run-first" look offensively, the Cowboys are more than happy to throw from alignments like this. They've had to get a bit more creative in designing mismatches in space because of the issues they've had throwing the ball from regular base formations.

Here's another example from their game against the Saints. This time the Cowboys are in 12 personnel with two tight ends on the field. Witten is lined up on the line of scrimmage with his hand in the dirt, and Gavin Escobar is flexed out wide to the bottom of the screen. Witten runs a quick "Stick Nod" route, and breaks free for a 28-yard gain.

The Eagles' defense has to be prepared for looks like this. They saw it in the Week 2 game at Lincoln Financial Field.

Down in the red zone on second down, the Cowboys came out in 13 personnel, with three tight ends lined up tight to the formation. That was the look early on, but then a quick motion before the snap reveals their true intentions.

Before the snap, Romo motions Escobar out wide to the left. Kiko Alonso travels with him. Alonso's combination of athleticism and length allows him to help defend this back-shoulder throw. This is why Alonso's return this weekend is huge for the Eagles' defense, to help deal with the heavy packages the Cowboys try to roll out to create mismatches in the passing game.

Think back again to that Week 2 game, remember the play Mychal Kendricks got hurt on? That was a play where Dallas went empty and spread the Eagles out. Running back Lance Dunbar ran a Go route down the left sideline against Kendricks. They ran the same play on the other side of the field against Jordan Hicks. They love to do these kinds of things to put linebackers in position where they have to play on an island against a player that they believe is a superior athlete. Lucky for the Eagles, with Alonso, Kendricks and Hicks, they've got three very athletic linebackers who they can use confidently in coverage at any point in the game.

Fran Duffy is the producer of "Eagles Game Plan" which can be seen on Saturdays during the season. Be sure to also check out the "Eagle Eye In The Sky" podcast on the Philadelphia Eagles podcast channel on iTunes. Prior to joining the Eagles in 2011, Duffy was the head video coordinator for the Temple University Football team under former head coach Al Golden. In that role, he spent thousands of hours shooting, logging and assisting with the breakdown of the All-22 film from the team's games, practices and opponents.