Like Four Verticals, Auburn has a number of other plays to stretch defenses horizontally. But rather than attacking safeties 20 yards down the field, they target the underneath zones the linebackers can't cover.
One way is to run option routes. Usually, the inside receivers use the Option route on the adjusters (linebacker, nickelback, etc.) while the outside receivers run the same Go/Comeback route they use in Verts. In that case, the inside receivers run five yards and then make a cut. If their adjuster is still inside, they will break outside away from that zone. If the adjuster is playing a zone coverage, the receiver will settle down in a gap between zones. If the adjuster is playing a man coverage, the receiver will keep running outside as he's being chased. And if the adjuster is responsible for the flat and gets outside quickly, the receiver can turn inside to get open. One route. Three options.
Auburn also has a simple All-Curl or All-Hitch play. Three or four receivers (depending on formation, protection, etc.) run six yards down field and turn around to fill up the space underneath with passing targets. Before the snap, the quarterback reads the defense's leverage on each receiver so that he has a good idea of which teammate will be open. Then, after the snap, he makes the shortest throw against the softest coverage. If a corner is playing press coverage, that receiver can decide to forgo the Hitch and convert the route into a Go, possibly turning a quick possession play into a home run.
You can see most of these options in this diagram I made for an earlier post. But the most common way Gus Malzahn targets this part of the field is with two short Comebacks, the 3-route on Malzahn's route tree.
Comebacks plus Verts
The playside receivers
The 9-man's job is to run a short Comeback at about 10 yards. Remember that a comeback is different than a Hitch or Curl in that the receiver widens toward the sideline after the break.
The 3-man's job is to run a short Comeback at about 5 yards instead of 10. The difference in distance gets both receivers to turn around at the same time.
The 4-man, like in most concepts covered so far, gives the quarterback a checkdown option, though this time it is more in the middle of the defense rather than toward the Will linebacker. Of course, this only applies if his reads don't indicate a blitz. Otherwise, he'll stay back to pick up an extra pass rusher.
As you might recall, Cover 3 and Cover 4 defenses don't leave many defenders in the underneath zones, so any of these so-called Spacing concepts is great against them. However, if the opponent is playing Cover 2, the offense is going to have a hard time finding open zones fewer than 10 yards past the line of scrimmage. So, when Gus Malzahn calls for two Comebacks to one side, he usually calls for the backside run a concept that destroys Cover 2. Four Verts.
The backside receivers...
In this play, the backside receivers run what the playside receivers run in 4 Verts. The outside receiver runs a Go and the inside receivers runs a Seam or skinny Post. Because the play isn't relying on these verticals to get open against multiple coverages, the post-snap reads that can change the Go to a Comeback aren't as important.
After the quarterback determines that he isn't facing Cover 2, he has a pretty easy read. In a non-Cover 2 defense, an outside linebacker is probably the flat defender. If this player gets outside quickly, the inside Comeback should be open. If that flat defender stays inside or takes his time getting outside, the outside Comeback should be open.
One of the best red zone plays for Auburn over the last two years is the pump fake and pass to C.J. Uzomah. The most memorable example is Auburn's last offensive play of the 2013 Mississippi State game.
Auburn had run the short Comebacks concept several times in the second half, so this play was set up well. (The GIF above is from the same game.) Jay Prosch and Uzomah ran their routes like normal while Auburn kept seven players back for pass protection. Nick Marshall pump faked as Prosch and Uzomah turned around, but Uzomah never intended to stop. He reversed direction again and Marshall found him in the back corner of the endzone.
Sammie Coates got a big reception in the 2013 game versus Texas A&M the same way.
When and where to use this play...
Obviously, these kinds of plays work well against Cover 3 and Cover 4 because there just aren't enough defenders in the underneath zones to cover every receiver. And the Hitch-n-Go is a great option for the red zone if the defense has seen plenty of Comebacks earlier in the game.
The Hitches and Comebacks don't work well against Cover 2, so the vertical routes are sometimes added to give the quarterback an option against that coverage. But do you remember that combo coverage Gus Malzahn labeled as one of the eight basic coverages a quarterback should be able to read? Cover 42, or Cover 4 to one side and Cover 2 to the other. The Comebacks-Verts play is practically useless if the Comebacks go the Cover 2 side and the Verts go to the Cover 4 side.
In fact, except for Four Verts, the concepts discussed so far are only good at attacking certain coverages along the sidelines. There will be times when a route combo gets matched up with defense it just can't beat. And we haven't really talked about man coverage. More importantly, we've largely ignored a whole third of the field. The middle third, which is where we'll go next.