Before we get into identifying coverages, we have to know a little bit about what the defense is trying to cover. The field is broken up into 9 different passing zones; three deep and six underneath zones. Zone coverages are designed for all of these areas to be covered. The diagram below shows you all 9 coverage zones.
On any passing down, a quarterback always has things to check pre-snap in regards to the alignment of the secondary. How the secondary is aligned can give us cues as to what coverage the defense will be playing post-snap. Having a good idea of the coverage being played gives the quarterback an idea of where he wants to go with the football before the ball has gotten into his hands.
When identifying coverages, the first indicator for the QB is looking at the number of deep safeties present. There can either be 0, 1, or 2 deep safeties. We refer to this as "middle of the field open" and "middle of the field closed" families of coverages. We'll first take a look at the MOFC (middle of the field closed) family of coverages.
Anytime there is just one safety between the goal posts, we call this middle of the field closed. That's because there is one safety in the middle of the field, closing down our throwing lanes. Here is an example of what this would look like.
The two main coverages in the MOFC family of coverages are cover 3 and cover 1, also known as man-free. Cover 3 is a zone concept that employs three deep zone and four shallow zone defenders. Cover 1 or man-free is a man coverage. We will first look at cover 3.
Cover 3 consists of three deep zone defenders and four underneath zone defenders, assuming the defense does not blitz and underneath zone defender. Here are the responsibilities of the different defenders in cover 3, along with cover 3's strengths and weaknesses.
As you can see from the diagram all 9 zones are assigned for. However, the OLBs are responsible for covering 2 zones apiece. The curl and flat areas are often where cover 3 defenses can be taken advantage of. Also, the FS has a lot of area to cover in the middle of the field. There used to be a lot more cover 3 played than there is today. One reason for this, is because teams are taking advantage of the cover 3 FS by stretching him horizontally with a four vertical concept.
Here are a couple more looks at what cover 3 looks like pre-snap.
Cover 1 or man-free
The other coverage besides cover 3 that can be played with the middle of the field closed is cover 1 or man-free. This is a true man concept with the FS having no responsibilities except to read the QB's eyes and make a play on the ball.
Here is a diagram of cover 1, along with it's strength and weaknesses.
You'll notice each defender has no zone responsibilities, but is manned up on a receiver with the free safety being a true "free" safety in this sense.
The difference between cover 3 and cover 1 pre-snap:
We've gone through the two most popular coverages in the MOFC family. So, how would a quarterback tell the difference pre-snap after identifying the one safety in the middle of the field? I teach my QBs the acronym D.E.L., which stands for depth, eyes and leverage. They are to next check the depth, eyes, and the leverage of the corners. In cover 3, the corners will be head up or have outside leverage and play at a depth of 8-12 yards. Their eyes will be looking in the offensive backfield, as it is a true zone coverage. In cover 1, the depth can vary, but is usually played at less than 5 yards depth. Their leverage will be inside to to take away the slant pattern, and their eyes will be fixed on the man they are covering. If you noticed on the cover 3 pictures, the corners are playing deep with their eyes in the backfield.
Defensive coaches have made it a point of emphasis to not make it as easy and clear cut as this. They are lining up with 2 safeties and playing forms of cover 3, they are lining up with one safety and playing forms of cover 2. However, when seeing one deep safety there is a very good chance one of these two coverages outlined will be played.