Four Verticals is a passing concept that is almost exactly what you'd expect: four receivers running vertical routes. The fifth eligible (usually a back) will check their protection responsibility if they have one, and then release into some sort of underneath route:
Image via Chris Brown, who has previously highlighted four verticals here and here.
While all of those vertical routes might look simple, the nuances of the concept are really what make it tough to stop
You'll notice in the diagram above that there are several sight adjustments to the play that receivers can make. Keep in mind that these are made when both the receiver and the quarterback recognize what the defense is trying to do and then adjust on the fly.
Outside receivers
The outside two receivers are usually only thrown to based on their matchup. When we are thinking about the Browns, we would probably only throw an outside route to one of our tight ends or maybe someone like Peyton Hillis if we could motion him out there and get him vs. a plodding linebacker. You are really looking for something like Calvin Johnson singled-up on a 5'9" CB to throw this.
Basically, if the WR can run by the corner, he will look for the ball over the CB but under the safety. If the CB turns and runs with the WR but has his head turned away from the QB, the WR should look for the back-shoulder fade and the QB should throw the ball through the CB's helmet.
Depending on the team, the outside receivers may actually break down and run some sort of curl route if the CB stays really high over the top like in Cover-3. Other teams will look to simply run the corners deep and go elsewhere with the ball.
Inside Receivers
Typically, one of the inside receivers is on a "locked seam", meaning he's running a seam route and probably only going to get the ball if the defense cheats away from him.
The second guy is running some sort of seam route with at least one sight adjustment to be made based on the defense. This route can be widely different based on the offense, but basically the receiver is looking for a pass just over any zoning LBs and in front of the safety, and he'll be looking to make a move inside, toward the middle of the field to get it or just staying on the seam if its MoFC.
The majority of the time, the seam reader will be the primary look for this play. He'll bet the ball not on a deep bomb, but on a quicker, medium-depth throw over the middle. Because he'll need to adjust his route based on what the defense does, he needs to have great chemistry with the QB.
Back/Underneath Receiver
The last guy in the progression is usually a back. He'll check his protection responsibility, and then release on either a drag or a hook or some other underneath route, usually headed toward where the seam reader started his route.
Even with the option routes by the seam reader and outside receivers, the defense may be able to have their underneath defenders drop off and "carry" the routes to deep defenders, who are waiting to help bracket the receivers and close any open windows in the coverage.
When that happens, the offense is in a great situation to get the ball to their back, who will likely be either singled-up or alone in vacated zones. "Speed in space." With all of the vacated space underneath, the back should be able to get open with room to run.
Browns vs. Jacksonville Jaguars
Of the games I've been able to study this year, I'd say we ran four verticals (or in West Coast Offense terminology, "Seattle") the most against Jacksonville. It shouldn't be surprising given our offensive struggles that it wasn't as successful as you'd like. In the example below, the verticals run the coverage deep and QB Colt McCoy doesn't see anything he likes down the field. RB Chris Ogbonnaya has plenty of room underneath, but Colt expects him to keep running while Ogbonnaya wants to sit down in coverage.
Note that we force the defense into a single-high look by using a trips formation (it's hard to run C2 against trips, but that's another post) This appears to be Cover-1 with a robber or a blitzer pre-snap. The coverage drops off except for one guy man to man with Ogbonnaya. He should run away from that guy, catch the ball while running, and be able to pick up some good yardage. Instead:
A second time, the coverage again drops off to cover the verticals. This time Colt and Ogbonnaya are on the same page and we get a good chunk of yards:
Five Vericals?
During the initial broadcast, I thought we successfully completed the ball to Greg Little on one of the four verticals. I'm not sure exactly what play it actually was, but it appeared that we were actually running FIVE verticals on this play. One was probably going to turn into a curl or sit route or some shallow-breaking route, but the play hit so quickly that it just looked like five verts: