When Chip Kelly initially made the jump from Saturdays to Sundays, his spread offense was put under the NFL microscope. The more college-y aspects received the bulk of the attention (and for the most part, still do) — the no-huddle, the tempo, the zone read. But as Smart Football’s Chris B. Brown noted prior to Kelly’s first NFL regular season in Philadelphia, the biggest question mark was always how well Chip’s passing game would translate to the pros.

Ron Jaworski, noted football prognosticator, didn’t think it would, calling Kelly’s passing game a "movement offense by the quarterback" that lacked "NFL passing concepts." Numerous others had their concerns as well, and rightfully so. After all, Kelly’s offense was, and still is, built around the running game; at the college level there wasn’t as much incentive to fully develop the passing game.

Kelly’s coaching staff hires on the offensive side of the ball in Philadelphia reflected an awareness of this problem. While some carryover from his days at Oregon remained, the collaboration with coaches who had extensive experience coaching the NFL passing game resulted in Kelly’s aerial attack featuring many of the same concepts we see utilized during every single pro game.

So much like the running game, there’s nothing revolutionary about Chip’s passing game. In fact, NFL passing concepts are largely homogeneous from team to team. While some teams might feature a few concepts more than others, the route combinations and basic principles are mostly the same. It’s the packaging of these concepts — personnel, formations, motions, etc. — that changes.

These passing concepts can be grouped into a few buckets based on how they attack the coverage: 1) horizontal stretches, 2) vertical stretches, and 3) triangle stretches. Some will add a fourth bucket for concepts tailored to defeat man coverage, but man beaters typically feature characteristics that still place them in one of the three buckets listed above.

Over the next few days, we’re going to cover the passing concepts that show up most frequently in Chip’s offense, how they attack the defense, and a few of the ways Kelly deploys those concepts on the field, beginning today with horizontal stretches.

All Curl

Horizontal stretches aim to overload the defense by spreading more receivers across the width of the field, at roughly similar depth, than the defense can cover. All curl is a classic example of attacking single-high defenses in this manner, as it distributes five receivers across the field for just four underneath defenders to cover.

All curl starts with the spot route over the middle. This is a rhythm route for the quarterback; if it’s open, the ball should be released on the final step of his drop. As Kelly explains while breaking down film for the Eagles’ website, if the spot route is covered the quarterback will move to a curl-flat combination on the outside based on how the defense takes away the pass over the middle.

With only four underneath defenders, the defense cannot account for the curl-flat combination on both sides of the field. Often, one of the inside linebackers will rotate over to take away one of the curl routes, giving the offense a 2-on–1 advantage to the opposite side. It’s this movement from the inside linebackers that the quarterback will read to determine what side of the field to focus on.

Once the 2-on–1 advantage has been established, the quarterback will read the flat defender to that side of the field. If the defender sinks to the curl route, the flat will be open; if he widens with the flat route, the curl will be open.

Proper route distribution is key, so that one defender cannot cover two receivers and negate the offense’s advantage. Kelly divides the field into five areas, one for each receiver. So long as each receiver makes it to their designated area of the field, the defense’s actions should lead the quarterback to the open receiver.

Mesh

Whereas the all curl concept looks to exploit the flat defender with a 2-on–1 advantage to the outside, mesh turns the quarterback’s attention inside. When facing zone coverage, the offense should gain a 3-on–2 advantage on the hook defenders in the middle of the field. Mesh also has numerous natural rub elements built in should the defense opt for man coverage.

Most coaches pair the mesh route combination — which consists of the two shallow crossing routes — with some sort of "alert" route deep. The quarterback will check the alert route for either a blown coverage or a favorable matchup right after the snap before coming back down to his progression in the middle of the field.

For Kelly, a wheel route out of the backfield frequently serves as the alert route. As Kelly explained on PhiladelphiaEagles.com, the use of the wheel route is all about creating mismatches against man coverage. "If we can get [the running back] in space and take advantage of a mismatch, then that’s what we’re trying to do on this play," Kelly said.

Take a peak up at the offense’s alignment in the image above; this is the look Kelly prefers to run the mesh concept from (though the personnel and how he gets to that look will change). By splitting two receivers wide to one side of the field, Kelly is looking to attract the defense’s two cornerbacks. If that happens, the defense must decide whether it wants to cover the running back with either a linebacker or a safety. If the answer is a linebacker, that’s a matchup Kelly expects his offense to win.

Should the defense successfully take away the alert route by getting a defender on top of the wheel — either with a defender making a good play in man coverage to sift through traffic and stay over the top, or by playing zone coverage — the quarterback moves off the wheel route and looks for one of the three receivers in the middle of the field.

Versus man coverage, it’s pretty straight forward. The rub element inherent with the mesh routes should allow one of the receivers to break free and separate across the field. If the defense is in zone coverage, the quarterback is reading what effectively becomes a triangle of receivers outnumbering the two hook defenders in the middle, moving from one shallow cross to the other before landing on the spot route right over the center.

Among the most interesting variants Kelly has for the mesh concept is to convert the two shallow cross routes into pivot routes.

"I think you just self-scout yourself, and we’ve run a ton of shallow crossers, double shallow crossers, where guys are running and crossing, and defenders understand that," Kelly said of the pivot variant. Once defenders begin to overplay those crossing routes, Kelly can dial up the pivot routes to leave them out of position.

The receivers who would have been running a shallow cross simply stick their foot in the ground once they get to the hash marks and break back toward the sideline. For the quarterback, nothing changes. He gets the same picture in the middle of the field, and goes through the same progression as before. But now the defense has one more thing to think about.

"If we’re continuing to run this and the defenders are always behind, then we’ll continue to run this [the standard way]," Kelly explained. "If the defenders start to get on top of us, then we have the ability to put our foot in the ground and come back out."

Four Verticals

When you think of stretching the defense horizontally, you typically think of plays like all curl and mesh: shorter routes that stretch the underneath coverage from sideline to sideline. But it’s also possible to outnumber the deep-coverage defenders in this manner, and there’s no better way to do so than with four verticals.

Four verticals is a landmark route concept — each receiver has a specific aiming point to reach, regardless of their initial alignment. The purpose of these landmarks is to create proper distribution of the receivers across the field and ensure that three deep defenders cannot cover all four receiving options.

Up to three of the receivers have the ability to alter their routes based on how the defense is playing them. At roughly 10 yards downfield, both outside receivers can convert their routes into a comeback if the cornerbacks stay over the top of the route. Many coaches will also have one of the inside receivers run a "seam read," which allows them to bend their route based on what the safeties are doing in the middle of the field, but I haven’t found anything confirming this is how Kelly teaches it.

Winning individual matchups is a theme that percolates Kelly’s offense, but it’s especially emphasized on four verticals. For the receivers, that means getting a clean release into the route.

"What we tell our guys is that you have to win. You have to win in your individual route, you can’t get held up getting down the field," Kelly explained on PhiladelphiaEagles.com. "Not only does he have to beat the defender, he wants to get stacked on the defender, and we’re going to throw it right over the top of him."

The outside verticals will be thrown at times when the matchup dictates — particularly against single-high man coverage such as Cover 1 — but four verticals really puts stress on the single-high safety in deep middle. He is the quarterback’s responsibility. "The quarterback has to beat the free safety," says Kelly. Simply, the quarterback wins this matchup by forcing the safety to commit to one of the seam receivers and throwing to the other.

Kelly adds another element to the play by frequently marrying four verticals with play action to pull second-level defenders closer to the line of scrimmage and open wider throwing lanes for the vertical routes downfield. It’s an ideal complement to Kelly’s run game. With the emphasis on the run game and the way Kelly manipulates the defense’s efforts in gap control, his offenses tend to see a lot of single-high safety looks as the defense attempts to get an extra man into the box. Four verticals is the perfect way to attack those defenses in the passing game.

Based on the film I’ve watched, there’s not a more fully fleshed out pass concept in Kelly’s arsenal than four verticals. He runs it from a bunch of different formations and personnel groupings. And because receivers are running to the same landmarks regardless of where they line up initially, the picture is always the same for the quarterback. Here’s a look at some of the more common four-verticals variants that Kelly will run:

Double Post

Another horizontal stretch that Kelly will use to attack a deep defender is the double post concept. This is a concept you will see Kelly dial up on the fringes of the red zone, as double post does a great job of attacking quarters and man coverage, two popular coverages in that area of the field.

Regardless of whether it’s quarters or man coverage, the "stretch" defender is the safety to the double-post side of the field, as he must choose to help on either the inside or outside post, leaving one man single covered. "We felt like when [the inside receiver] runs a post in [to the middle], he’s going to occupy two [defenders]," Kelly explained on PhiladelphiaEagles.com. "Really what we’re trying to do is isolate our outside receiver on a corner."

Getting width on the route stem is key for the outside receiver. This threatens the cornerback’s technique, potentially forcing him to open his hips outside and lose leverage, and widens the throwing lane for the quarterback. On the break, the receiver cuts across the defender’s face to regain inside leverage. It’s unlikely that the receiver will end up wide open on this play; he must win the ball on what will likely be a contested catch. As Kelly says, "1-on–1 doesn’t mean you’re covered, it means you’ve got to go make a play."

"We tell [the quarterback], the tighter the coverage, the lower the throw," Kelly says of what is expected from the quarterback on this throw. "If it’s up high, [the defender] has an opportunity to pull the arms away and strip it. But if you put it in the framework of his body, it’s really just low-post basketball."

Like most passing concepts, double post can be run from several different formations, but Kelly really likes it from a bunch look, such as the one shown in the images above. With the No. 1 (outside most) and No. 3 (inside most) receivers in the bunch running the post routes, they should be afforded clean releases on most plays.

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Horizontal stretches make up a relatively small portion of Kelly’s passing game, which consists of over a dozen different concepts that he goes to on a regular basis. What Kelly really wants to do with his base passing game is stretch the field vertically and push the ball downfield, which we’ll start exploring in tomorrow’s article.