Sunday's game is going to be an incredible test for the Philadelphia Eagles for a number of reasons. The Chicago Bears offense is as formidable an offensive attack as they've seen all season long, and that includes their Week 4 matchup against Peyton Manning and the Denver Broncos.

Obviously, a lot of the talk has circled around the dynamic duo of Brandon Marshall and Alshon Jeffery. Both of them are big receivers who can get down the field and win every jump ball thrown in their direction. To kick off this piece, however, I want to take a look at how they impact the running game. The Bears are 13th in the NFL in rushing yards per game, 8th in rushing yards per play, and with the ever versatile Matt Forte coming out of the backfield, they will always be a threat on the ground.

It's first-and-10 against the Minnesota Vikings, and the Bears come out in 21 personnel with two running backs, a tight end and two receivers. You have Jeffery to the right, and Marshall at the top of the screen to the left.

At the snap, this will initially look to be a lead play (one of their favorite downhill runs) with fullback Tony Fiametta blocking for the running back, in this case Michael Bush. What actually happens, however, is that Jeffery comes around on the reverse, with Fiametta coming across the formation as a lead blocker on the perimeter.

The defenders in the box hesitated thanks to the run fake inside, and now with Jeffery on the perimeter, look at the wall that's set up. You've got a seal from center Roberto Garza (circled), a lead block from Fiametta and a great job down the field from Brandon Marshall. This turns into a 38-yard gain and a first down for Chicago, as Jeffery makes a play in the run game. The threat of Jeffery making an impact on reverses is real and something defenses have had to account for all season long. That was apparent in the team's Week 8 matchup against Green Bay.

It's first-and-10, and before the snap the Bears are going to send Jeffery across the formation as if he will be running a jet sweep, taking a handoff from quarterback Josh McCown.

Three Packers defenders react to the jet sweep-action and flow to that side of the field.

What you're getting instead is a quick "flip" play to Matt Forte, who has a lead blocker in the form of left tackle Jermon Bushrod, and a wall is created by the receivers on the outside. The Bears love to get Forte on the outside in space, and this "flip" play is one of their favorite ways to do it, and it's one they go back to repeatedly out of different formations.

Take this play, for example. It's once again first-and-10, and the Bears are in 21 personnel. You've got a two-back set with Michael Bush lined up as the fullback and Matt Forte as the tailback. With Bush and Forte in the same backfield, the defense has to be aware of the different threats both backs present. At the snap, it's going to look like a quick handoff to Bush inside, but this will actually be the same type of "flip" play to Forte, this time to the right.

This was a great play call, especially against the Lions and their defensive line, known for being aggressive down the line of scrimmage (remember the old "rush, crush and close" philosophy?). The defensive end, Willie Young, bites down hard on the run action, and right tackle Jordan Mills (circled) seals the front side. When Forte takes the pitch, he's got the seal and two blockers out in front, Jeffery and Marshall.

This is the other impact you see from these big receivers in the run game. You can tell they take a lot of pride in their role as blockers down the field. In the circle to the right, Marshall gets his man to the ground. In the left circle, Jeffery takes not one but two defensive backs out of the play, giving Forte enough room to go 53 yards for a touchdown.

Multiple times this year, we've talked about other teams' use of "packaged plays" that have been prevalent here in Philadelphia since the arrival of Chip Kelly. I broke down that exact concept for Eagles Gameday Magazine a couple weeks ago.

It's late in the fourth quarter against Washington, and the Bears are running that exact concept against the Redskins. The inside zone, pop pass and bubble screen options  are all available for quarterback Josh McCown.

At the snap of the ball, McCown reads the weakside linebacker. He plays downhill towards the line of scrimmage, creating space behind him for tight end Martellus Bennett, and it's an easy throw and catch for six points. This is a perfect example of a read option concept on full display resulting in a big play for Chicago.

But is it a "packaged play" every time we see the bubble screen and pop pass from the Bears? Here's a play Chicago ran this past Sunday against Cleveland.

It's first-and-10, and again we see the very same look at the snap of the football – Martellus Bennett down the seam, Alshon Jeffery in the slot on the bubble pass, and an inside zone run from Matt Forte. The routes take place, but is this actually a "read option" packaged play?

Upon further review, that does not, in fact, appear to be the case. While the Bears do run those "packaged plays" from time to time, it's not always a post-snap read for the quarterback. This time it was a run play from the jump, and it was a look they showed several times against Cleveland. So why run the pop pass and bubble screen action if you're just running the ball anyway?

Well, there could be a number of answers to that question. It could be that it's a pre-snap read (not post-snap), much like the play we saw from Tony Romo this Sunday when he threw his first interception of the fourth quarter against Green Bay (a play I broke down here). The more likely answer, in my opinion, is that those routes are pure window dressing. The defense still has to account for it, and you're drawing defenders away from the play by running that action. Above, you see the defensive end (No. 93) working outside to defend the pop pass. Out of the frame, the slot defender has his back to the play as he covers Jeffery on the bubble screen. You're removing defenders from the action and creating scenarios where you have more space for your playmakers to make plays. This is a simple concept, and one I would expect to see on Sunday night at Lincoln Financial Field.

Staying with the run game, I would be remiss if I didn't mention the job that the two rookies on Chicago's offensive line have done thus far in 2013. Much was expected of first round pick Kyle Long, the right guard, a former pupil of Chip Kelly at Oregon. He has played very well to this point. Fellow rookie Jordan Mills, the right tackle from Louisiana Tech, is an even greater story. When he was drafted in April, the team had J'Marcus Webb, Gabe Carimi and Jonathan Scott on the roster competing for that spot, and he beat them all out. Both players have been an integral part to the Bears' success on the ground and through the air, and they will be building blocks for them moving forward.

Focus on former second-round pick Eben Britton (circled). In talking with Greg Cosell this week, he told me that nearly 20 percent of the Bears' snaps will feature Britton on the field as an extra tight end. Whether he is on the field alongside Martellus Bennett (like he is on this play) or in place of Bennett in one-tight end sets, bringing in Britton allows for another stout blocker up front in the run and pass game. Here, Britton is a blocker at the point of attack in the run game.

Look at the hole he and Bennett open up for Forte, who fires through and gets downhill for a 35-yard gain.

Here's Britton against Cleveland. He's lined up next to Bushrod and will help in pass protection. The Bears will be running play-action (look for that with Britton in the game), and attacking the Browns defense down the field.

This is going to be a three-level stretch from Chicago, as they send Alshon Jeffery on a deep corner route. That, combined with the route from Brandon Marshall on the outside, will serve as a "hi-low" combination on the cornerback at the top of the screen.

The corner stops to stay with Marshall, and Jeffery has plenty of room behind him to go and get the football as Jay Cutler leads him towards the end zone.

We talked a lot about "high-low" concepts last week preparing for Minnesota, and Chicago likes to run a lot of those same concepts to get their receivers open in space down the field.

It's second-and-10, and at the top of the screen the Bears are running a dig-post combination (one of my favorite route combinations) with Jeffery and Marshall. First, notice the alignment of both receivers before the snap. Outside, you have Jeffery, who is running the 12-yard dig route over the middle. Inside of him, you have Marshall running the deep post over the top. At the snap of the ball, however, you'll see them switch, with Jeffery coming inside and Marshall outside. This "switch release" is a common theme from the Bears' deep passing game.

The ball is snapped, and we see the deep safety in a bind. He can sit back and defend the post or crash down on the dig route. He decides to drive down, and Cutler floats a beautiful pass over his head for a 44-yard pass to Marshall down the middle on the post route. Perfectly designed and executed by the Bears offense, and another example of a "high-low" combination.

Last week I broke down "china" concepts in the passing game, something we not only saw Minnesota do a lot on tape but also saw the Eagles use to their advantage to get DeSean Jackson open for his touchdown last Sunday afternoon. Basic principle: Jeffery runs a short in-breaking route to hold the corner underneath, giving Marshall plenty of space over the top on his corner route.

This play works to perfection, as quarterback Josh McCown has a ton of room to drop the ball in to Marshall, who makes a great leaping grab at the front pylon for a touchdown.

Lastly, the Bears LOVE to attack opposing secondaries by challenging them down the field with multiple vertical routes. Much like we saw with the Denver Broncos, you will get a lot of "all go" looks with three and sometimes four receivers running straight down the field, a problem for teams that typically play with a single high safety (this forces that safety in the middle of the field to decide which side to lean towards, opening up space on the opposite side).

It's second-and-8, and Jeffery, Marshall, and Earl Bennett are all attacking the defense vertically.

But you'll also get running back Matt Forte leaking out of the backfield. Forte is a great player for the Bears in passing situations because not only is he a great blocker in pass protection, but he is a great receiver out of the backfield as well and a weapon in the open field.

Very much like we saw the Eagles use DeSean Jackson a week ago, running a set of vertical routes to clear out space underneath, the Bears love to attack the defense vertically to create room underneath for Forte to do work on the open field. Look at the room Forte has when he catches this ball as he turns, makes one man miss and takes it for a 33-yard gain.

The Bears defense has had its share of issues under new coordinator Mel Tucker. While this unit may rank last against the run and 28th in points per game, there are still some very talented players on that side of the ball, and Tucker does a lot of things schematically that are tough to prepare for.

It's third-and-6 against the Pittsburgh Steelers, and the Bears have eight players right on the line of scrimmage, including both linebackers, their nickel corner and safety along with four down linemen. The Steelers have to decipher how many players are coming and where the pressure is coming from in a matter of seconds. This is not easy for quarterback Ben Roethlisberger or the offensive line.

This will be a six-man pressure, with two players dropping off the line and the rest coming after the quarterback. There are a lot of moving parts to this blitz, and it isn't just up front.

This will be a three-deep look from the Bears, but the designated free safety before the snap is not going to be the deep safety after the snap. One of the players highlighted in the previous shot, Chris Conte (No. 47), will drop off the line of scrimmage and fall all the way back to the deep third to defend the post. That, combined with the two cornerbacks on the outside, gives you a three-deep coverage.

The Bears will have two underneath defenders on this play. One is linebacker James Anderson (No. 50), who buzzes out from the line of scrimmage at the snap of the ball. The other is the player who lined up as the deep safety before the play started, Major Wright (No. 21). This safety rotation, paired with the stunts and pressure up front, confuse Roethlisberger and the Steelers offense.

Roethlisberger sees the pressure and knows he has to get rid of the ball quickly. He gets the ball out of his hand to his safety valve, Jericho Cotchery (No. 89), who was lined up tight to the formation. Roethlisberger doesn't see the safety rotation and thinks this will be a quick completion to beat the blitz and get a first down. Instead, this is an interception for Wright, who picks the ball off and returns it 29 yards for a score.

The Bears' leaky run defense can be attributed to a number of factors. They've had a lot of injuries both at linebacker and defensive tackle and have had to rely on a number of young players at every level of the defense to step up and play. But one of the most glaring issues is angles in the defensive secondary, and Chris Conte has been one of the most consistent culprits. The result: Tons of big plays for opposing running backs.

It's first-and-10, and the Bears again will rotate safeties here, this time going from a two-deep shell to a single-high look with Conte as the post safety.

The Packers run the ball, and rookie Eddie Lacy powers through the line of scrimmage. It will be up to Conte, as the last line of defense, to bring Lacy down for a short gain.

Instead, Conte takes a bad angle, and Lacy (not exactly known for his blazing speed) blows past him for a 56-yard gain to set up a touchdown. This has been a bad theme for the Bears secondary in 2013, and against an Eagles offense that forces you to win one-on-one battles in the run game, taking proper angles will be a key for the Bears defense on Sunday Night Football.

Fran Duffy is the producer of the Eagles Game Plan show which can be seen on 6abc Sundays at 11:30 AM. 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.