Philadelphia Eagles' offense: What's curbing Chip Kelly's attack?

What's wrong with the Philadelphia Eagles' offense?

That's the question many observers are asking after watching Chip Kelly's unit struggle over the past two weeks. Despite sporting a 4-1 record and scoring 30-plus points four times, the Eagles' high-flying offense has been grounded by rough-and-rugged defenses in consecutive games. Philly didn't score a single offensive point against the San Francisco 49ers in Week 4, and the offense looked underwhelming against the St. Louis Rams in Week 5. Nick Foles and LeSean McCoy, both Pro Bowlers in 2013, have put up pedestrian numbers all season. Have opposing defenses discovered the formula for stopping Kelly's spread attack?

Given some time to dig into the All-22 Coaches Film, I unearthed three main reasons why the Eagles' offense has lost some of its potency in 2014:

1) Defensive coordinators have caught up with Nick Foles.

The NFL is full of bright football minds, so it rarely takes long for astute coaches to adjust to personnel/schemes when they've had enough time to study the film and assess tendencies. Defensive coordinators spent the offseason breaking down Foles' play within Kelly's system and crafted effective solutions to deal with the Pro Bowl quarterback.

From a scouting perspective, defensive coordinators understand that Foles is a limited athlete without the speed, quickness or agility to threaten the edge as a runner. Thus, they are ignoring him on the zone-read and committing more defenders to attack LeSean McCoy in the run game. Against the pass, defensive play callers are using more blitzes, stunts and games to create penetration up the middle, leading to Foles throwing balls with defenders in his face. As a result, Foles is fading away on his throws and delivering floaters to his receivers over the middle. Although he has gotten away with many of his "toss-ups," Foles' willingness to throw the ball into traffic under duress has led to his bloated INT number this season (five already, as opposed to two during the entire 2013 campaign). With teams across the league watching Foles seemingly crack under pressure, more defensive play callers will turn up the heat to see if they can force the young quarterback into poor decisions from the pocket.

Foles also has struggled with his accuracy and ball placement on deep throws. He repeatedly has been off the mark on vertical routes, preventing the Eagles from cashing in on some big-play opportunities. While Foles certainly deserves his fair share of criticism, the Eagles' receiving corps hasn't helped him much, failing to get significant separation downfield. Looking at the tape against the 49ers and Rams, I rarely saw a receiver win a one-on-one matchup on a vertical route. As a result, Foles is forced to fit the ball into tight windows, and 50-50 balls don't always work in his favor.

Let's examine a couple of plays from this past Sunday that show how the wideouts' lack of separation really hurts the quarterback ...

In the play depicted just below, Jeremy Maclin is aligned on the outside of a trips formation to the right. He is instructed to run a go-route against Rams rookie CB E.J. Gaines. However, Maclin is unable to run past Gaines with straight speed and fails to use a double move or stutter-step to force the young defender to hesitate. As a result, Gaines is in perfect position when the ball arrives and makes an easy interception on an ill-advised throw by Foles (TO VIEW THE PLAY, SCROLL LEFT TO RIGHT ON THE IMAGE BELOW):

With Foles unable to connect with his receivers on vertical throws, defensive backs are increasingly jumping the Eagles' short and intermediate routes. Although the ultra-aggressive tactics leave defenders vulnerable to double moves and deep throws, many opponents are willing to push the envelope and force Foles to make tight-window deliveries.

In the next play breakdown, the Eagles are in a dubs formation with all-hitches called in the huddle. The four receivers will stop their routes at about seven yards, aiming to give Foles an easy completion against St. Louis' man coverage. But Rams defenders aren't afraid of vertical routes by Eagles receivers, so they are aggressively squatting on the short routes. Without enough space to fit the ball into his receiver on the right (Maclin), Foles is forced to throw wide to avoid an interception by the hard-charging defender (TO VIEW THE PLAY, SCROLL LEFT TO RIGHT ON THE IMAGE BELOW):

Foles hasn't played at a Pro Bowl level this season due to the new tactics opponents are throwing at him. From various pressures and blitzes designed to make him uncomfortable in the pocket to defensive backs aggressively jumping routes, the quarterback is facing constant harassment at every level. With these ultra-aggressive strategies resulting in an alarming turnover total from the Eagles QB (eight, including fumbles), opponents will continue to ratchet up the pressure until Foles performs better from the pocket.

2) Defenses are selling out to contain LeSean McCoy.

For all of the attention Foles received for his spectacular play in 2013, it was McCoy who served as the driving force of the offense. The 5-foot-11, 208-pounder easily led the league in rushing (1,607 yards), displaying an electric running style that perfectly matched the Eagles' dynamic scheme. McCoy attacked the middle of the defense on inside-zones with his explosive quickness and burst, yet displayed the ideal combination of patience, speed and acceleration to turn the corner on outside runs. As a result, McCoy posted nine runs of 20-plus yards and three of 40-plus in 2013.

This season, however, McCoy hasn't been able to get into a groove as the Eagles' feature back. He is averaging just 2.9 yards per carry -- down from 5.1 last fall -- and has one run of 20-plus yards in five games. Stunningly, he has yet to crack the 100-yard mark in any game and his disappointing production has grounded an Eagles offense that was expected to rank as one of the most potent units in the league.

Poring over the tape of the Eagles' most recent games, I noticed defenses are committing more defenders to the box to slow down McCoy. Opposing coordinators are putting eight defenders near the line of scrimmage against the Eagles' two-back/heavy formations and keeping at least seven defenders in the box against one-back sets. Without a legitimate running option at quarterback, the extra defender allows opponents to clog all of the lanes at the point of attack.

Let's take a look at some examples ...

In the following screengrab, the 49ers are aligned in a 3-4, with the safety walking into the box to create an eight-man front against the Eagles' one-back formation. The 49ers have outnumbered the Eagles at the point of attack by alignment prior to the snap:

Each defender is instructed to fill a gap along the line, which creates an impenetrable wall:

With McCoy unable to find a seam in the defense, the 49ers are able to hold the electric runner to no gain:

In the next screengrabbed play, the 49ers are again aligned in a 3-4 against the Eagles' one-back set. Safety Antoine Bethea is dropping into the box to create an eight-man front prior to the snap:

Once again, the 49ers have outnumbered the Eagles at the point of attack and assigned a defender to every possible gap along the line. This tactic eliminates running lanes for McCoy and forces him to bounce around looking for a crease:

With Bethea closing quickly to the alley on the back side, McCoy is limited to a moderate gain on this play:

The Rams also used double-crash blitzes to contain McCoy. In the next play, cornerback Janoris Jenkins will crash off the edge, with defensive end Robert Quinn slanting inside the offensive tackle. Safety Rodney McLeod is also blitzing from the wide side of the field to create more chaos for the offensive line. Quinn blows past the offensive tackle to create immediate penetration. Jenkins and McCleod also come free on their blitzes to seal the edges and prevent McCoy from bouncing outside on the play. This results in Quinn recording a tackle for loss (TO VIEW THE PLAY, SCROLL LEFT TO RIGHT ON THE IMAGE BELOW):

Obviously, clever scheming from opponents has prevented McCoy from getting loose, but the Eagles' O-line woes have also been a factor. Philadelphia has played without three key blockers (Evan Mathis, Jason Kelce and Lane Johnson) early on, and the lack of continuity along the line has disrupted the rhythm of the running game. While Matt Tobin and David Molk have been adequate replacements up front, they certainly are not premier players. Thus, the Eagles have struggled mustering running room when facing elite defenders at the point of attack. Given the disruptive impact penetration has on a zone-based running scheme, McCoy's backfield dancing has been a matter of survival -- not an electric player trying to do too much with the ball in his hands.

3) With no DeSean Jackson, Philly's passing game lacks explosiveness.

Kelly might downplay the impact of Jackson's absence, but there's no doubt in my mind that this has been a big part of the offensive struggles. Jackson was one of the most explosive playmakers in the league during his six seasons in Philadelphia. He tallied 105 receptions of 20-plus yards and 35 receptions of 40-plus, scoring 39 total touchdowns (32 receiving, three rushing and four on punt returns). Jackson was a dynamic weapon in Kelly's scheme last year, posting career highs in catches (82) and receiving yards (1,332).

Without Jackson on the field to command the defense's attention, opponents are committing more defenders to the box to stop McCoy and daring the Eagles' receivers to win against man coverage. Now, I know Maclin is supposed to fill the void created by Jackson's departure, but he is coming off an ACL injury and not nearly as explosive as his former teammate. Thus, defensive coordinators are willing to concede a few plays to him on the perimeter if they can neutralize McCoy on the ground.

Looking at the Coaches Film from the past two games, I've seen teams use more Cover 1 (man free) and Cover O (man without a deep safety) to suffocate the passing game.

In the screengrab that follows, the 49ers are playing Cover 0, with five defenders locked onto the Eagles' five eligible receivers. The linebacker is playing the "low hole" to take away any crossing routes over the middle of the field. The 49ers are bringing pressure with five rushers on the play:

Despite playing "off" coverage, the 49ers are able to blanket the Eagles' receivers in man coverage. The "lurk" linebacker is looking for work with the running back heading to the flat:

Foles waits for his receivers to come open, but no one wins despite the 49ers leaving the deep middle open:

Eventually, Foles throws an incomplete pass.

Without a speedster on the field to blow past the defense on a vertical route, the 49ers were comfortable locking up the Eagles in man coverage.

San Francisco also played Cover 1 Lurk with a safety dropping down in the middle to take away any crossing routes. In the next screengrab, safety Eric Reid is the designated "lurker," with Bethea playing in the deep middle:

After the snap, the Eagles run a crossing route, as anticipated. Reid switches responsibilities with cornerback Perrish Cox and jumps Jordan Matthews on the shallow cross. Cox replaces Reid as the "lurker" and looks for a crossing route or dig coming from the opposite side:

Thank to fabulous execution/communication, the 49ers have Philly's receivers completely covered:

Without an open receiver to target, Foles scrambles a bit before tossing a jump ball down the field in Maclin's direction that falls incomplete.

The Eagles' lack of explosiveness on the perimeter has encouraged more teams to play man coverage and the results have been decidedly in the defense's favor. With a tough divisional bout on tap against the New York Giants, I'm curious to see how Kelly tweaks his scheme and personnel to combat the tactics that have grounded his offense in recent weeks.

Follow Bucky Brooks on Twitter @BuckyBrooks.