Now that we've gone over some of the basics on leverage and the terminology, we'll go into the pass concepts that an offense uses to attack a defense. In the following diagrams that I've constructed, whats important is the idea of how the offense attacks, not so much the actual route combination (pattern) they decide to run to accomplish it (though in some cases that is important, like the Smash). So if you just understand the concept, learning the routes and reacting to them is the next step. As a casual fan you don't need to know the routes they use (though we will go through some of this later), just try to understand how the offense draws up plays to go about it.
You'll see below that it really doesnt matter what formation the offense throws at you, all thats necessary to know is the way they'll attack. Once you understand that, you'll see that their formation only dictates how you align, not how its defended. What we'll show is the concept and a brief explanation of what they are trying to do.
Using terminology we've established before, but will reiterate again briefly.
H/C - Hook/Curl zone, the middle zones underneath the deep defenders. There are 2 or 3 middle zones combined together in some form (see diagram below), usually covered by a LB or SS. The Curl/Flat zones are self-explanatory, but can be covered by DEs, LBs, Corners, or SS. That assignment depends on the actual coverage called.
Route descriptions we've discussed before here.
WR counting - In terms of defense, it doesnt matter what the receiver plays as his position on the field (like TE, Flanker, RB, etc), all you care about his his position inside or outside and the number of eligible receivers on that side. Defenders can count either from the weakside all the way over (1-2-3-4-5) starting with the widest WR, or just count on their side of the formation. I do the latter, so X - A are 1-2 on the weak side (usually) and Z - TE are 1-2 on the strong side.
Vertical Stretch - The offense is attacking on different levels to make the deep defenders cover someone, and present a problem for the guys underneath by sandwiching them between receivers above and below. Basically stretching the zones in a vertical direction.
Horizontal Stretch - The offense is trying to flood zones with multiple receivers or make the underneath defenders slide over a long distance from the area they are assigned to cover.
Concepts
Hi/Lo - A vertical stretch. Probably the easiest to understand and most difficult to cover because the defender must be very disciplined. What they want to do is suck the underneath defender (LB) down to attack that 5-7 yard route, and make the defender take his body out of the throwing lane to the deeper route. The 15 yard route is the intended primary receiver, he'll take the 5 yard only as a checkdown. A quick change is to have the deeper route be a Dig/In route, and having him just work to the Hook/Curl area the underneath defender is trying to cover, so you have him moving on the catch. In general though the Hi/Lo can use just about any route other than a fly.
3 Out for the Curl - A horizontal stretch. The offense uses the route by the TE and RB in the flats to create an open space for the Z receiver running a curl route at about 15 yards. Here the H/C defender has to take the seam route, and the Flat defender must go to the back, but the seam route may distract the Corner and the Safety, getting the Z a hole.
The dotted lines in the below diagrams just depict how the routes may vary. The TE is supposed to break at 8 yards and depending on the read progression can be the primary, Z is #2 and RB #3. Otherwise the Z is primary with a 12-15 yard curl.
Normally the way its played is Cover 2 or Cover 4 with bracket (inside-outside) coverage by the Corner and Safety. Against Cover 3/4 the TE runs the Fly, and on C2 he'll usually curl.
3 Out for the Dig - A horizontal stretch. Similar to above, and again the 15-20yd Dig route is the primary. The seam route is meant to clear the area by pulling the H/C defender deep, and taking his body out of the throwing lane to the Dig.
3 Out Overload - The offense is attacking on 3 levels and overloading one side of the field. They are trying to pull the flat defender down to take away the RB, and open up the 15 yard Corner route by the TE below.
Bootleg - A vertical and horizontal stretch. The low crosser (FB/H-back below) must be taken by the H/C defender at an intersection point on his 10-15yd route. The flat defender is a primary threat to the defense, and the deep crosser is usually secondary, so the safety cannot cheat up. Blocking scheme by the front is intended to fool the underneath defenders, as usually a counter-trap (run) scheme, this lets the H-back get a free release.
As most of you know, Clemson runs this exact play below several times per game.
Flow Pass - The play-action fake keeps the MLB up and creates a hole for the Dig route, the Post is intended to clear the deep safety.
This video is very similar to the play above, Clemson was in max-protect which takes away the safety valves until the play develops further. Steve Spurrier uses the same play from different formations quite often.
Hooks - If the back goes Strongside, the backside slant can actually be the primary receiver for this play. All the strongside routes are hooks or option routes (WR can break either way). The RB is intended to control the flat defender while the routes are meant to get a hole open for the #2 and #3 receivers.
Double Crosses - The underneath stretch is meant to get the deep receivers open, and the slot receiver has the option of breaking to the left or right at 10-15 yards once he reaches the middle of the field. The backside defenders cannot pass off their receivers too early. The Weakside LB who would be matched on the Slot WR in the below diagram has to maintain his leverage and not let the "A" get inside him, he must try to wall him off.
The Slot WR will then try to go behind the MLB, so he must get depth in his drop and attempt to not get sandwiched by crossers.
This type of play is a backbone play of the Mike Leach Air Raid system.
Out/Slant - a blitz beater. the inside receiver quickly breaks outside, intended to open up the slant.
Double Slants - The receivers take a larger than normal split, if #2 is covered, then #1.
Outs - A quick 3-step drop play designed to get the ball to the inside receiver to the front side, in the diagram below, the TE. Z is trying to clear off the flat defender for the TE to catch and cut up field. The backside short option route by the slot is the secondary receiver. If changed to a 5-step drop, the QB will go in a rollout action.
Smash Concept - The classic Cover 2 beater shown below. I've also shown how the defense is supposed to take the route assuming it is Cover 2 ZONE (not 2-man), where the CB is the flat defender. As you can see if he is supposed to take the flat, he's stuck in a hi/lo stretch when he sees that inside receiver cut for a corner/flag route. The offense wants him confused and thinking which guy to take for just a second to get one of them open. The hitch route is generally intended as the primary.
Below is the accepted way to cover the smash combination, in pattern reading. The CB gets depth and if he sees the inside receiver breaking into the seam behind him, he must continue to drive deep. The H/C defender is the key, he must run up the seam initially, and yet watch the outside receiver. He only stops his drop when he sees #1 stop for the hitch. If he breaks off the #2 too early, he'll cut for the corner route.
Chris Brown at Smartfootball has developed the Smash concept at length, available here, and shows how it is able to defeat Cover 3 as well.
All Option - A "just get open" concept, where the receiver breaks away from the technique/alignment of his defender. If he shades you inside, you break outside, depicted below. if he shades your outside shoulder, you break inside. The 4 receivers are intended to split as far apart from each other as possible to try to isolate the defenders.
Scissors - A Cover 2 beater, designed to confuse the deep defender(s) to that side. The corner route is the intended primary receiver, and the Back is just a checkdown if its not open. The two routes are meant to cross at 10-15 yards, and the #2 must sell a post before breaking on the corner route, and sometimes "set a pick" like in basketball, which would help one get open.
If its Cover 2, the Cornerback sinks til #1 breaks on the post and the safety takes the Corner route. The mixup and delay is meant to get the inside receiver a chance to get open.
If the defense is playing Cover 3, the X receiver is breaking into the seam between the CB and FS, but the CB must also watch #2 who is breaking into his deep third, for example. The correct defense is to get the H/C defenders depth to stay under the post route and force a throw over their heads and hope the FS can get there. The flat defender must take depth initially and then take the back. The Cornerback has to take the corner/flag route from the A. It ends up not being a great route to throw against Cover 3 unless you have something to distract the middle FS on the opposite side, so he doesnt see the post coming.
Trips Seam Read- Vertical stretch and overload on one side. The #3 receiver is breaking in on the play unless the seam is given to him, so basically he looks off the safety. This is meant to free up a throwing lane to the #2 receiver (A below). The RB is the checkdown route.
4 Verticals - In this vertical stretch, the #2 receivers (seams) to each side are the primary, and the QB is meant to look off the safety. One of the two should be open against pretty much every Cover 3, the seams of which I've depicted in the diagram. If it were Cover 2, you can make the outside guys primary, but its similarly effective. Cover 4 or Cover 8 should be the best way to defend this particular play.
Another Chris Brown interview with Dan Gonzalez, author of Concept Passing, on the 4 Verts concept.
In the video below, Dabo Swinney explains Clemson's protection schemes against Odd (Nose guard) and Even (no nose guard) fronts, and you see several of the plays we run including 4 verticals, double slants, and a Smash.
Clear and Cross - The underneath crosser (TE below) is the primary. The backside will be trying to clear their side of the field with a vertical or out-n-up route and pull away the H/C and flat defenders. The crosser has the option to turn back to the other side of the field if he's walled off. The deep dig route is the secondary receiver (a vertical stretch). This is a critical concept used in red zone offense.
In this video Steve Logan details a play and blitz pickup, but the pass play instructed uses the above concept.
All-In - A Trips Hi/Lo Concept. The primary is either the #2 or the #3 receiver on the move, and the hitch is the outlet. The two receivers are trying to hi/lo the defense with a vertical stretch, and confuse the H/C defenders. Any hesitation on leading/trailing will open up one of the routes.
Clear Option Smash - A typical bunch pattern used by 3 receivers bunched together in the formation. The "A" below is trying to clear the area of the seam defender and open things up with an option route, meaning he can break either way based on the position of the safety. The back underneath is meant to pull the flat defender down, and together these two are trying to open a hole up for the hitch route by Z. The "A" usually won't get the ball unless there is a major defensive breakdown, and the RB is a safety valve.
Trail Concept - The 2nd receiver trails the 1st and breaks off his rear to either direction that is open. As you can see, the first receiver is trying to clear the area, and make the seam defender go with him. This should leave an opening underneath for the RB, who is the primary receiver on the play.
So thats several of the many concepts you can throw at a defense, Nick Saban has pages and pages of patterns in his defensive playbook and its these patterns and how defensive coverages adjust to the above concepts that we'll cover next.