Cover 3 is a Zone defense where three defenders (usually two cornerbacks and one free safety) split the secondary into thirds. No matter the play, each guy stays in his zone.
The corners take the deep outer 1/3rd’s and the Free Safety, the middle 1/3rd. They line up from about 12 yards off the LOS. Why 12? If you’ve been reading our series on WR routes, then you’ll know that deep routes begin between 12-15 yards down the field. Hence, the DBs line up at this depth.
Once the ball is snapped, all three guys adjust their depth depending on what they see. They each have a lot of ground to cover the further away from the end zone, so if they’re running this, the DBs better be some fast and tall dudes.
The Strong Safety plays up closer to the linebackers and plays a curl/flat zone, as does the Will-backers. This formation is best served with the front seven (plus one) being stout. Or you have a weak DL and you need the SS for extra thump. Either way, the idea is your back three are good enough to handle any pass, the front eight will stop any run, and rush the passer.
In the 3-4, the pair of Inside Linebackers have middle/hook zones more times than not when the defense is in a Cover 3, but there are variations where the SS and LBs are playing various man/zone combos.
If an extra defensive back is added, he’s called a nickel back. Yes, sounds of old alt rock is filling my head. Anyway, this nickel back can be a corner or safety depending on the play. If a nickel back is added, another player needs to be removed. That’s going to be the next article in the series. Nickel and dime formations.
Moving on, Cover 3 is a staple for many teams, but it’s not great against a vertical passing attack team. Like ours will be (Halle freaking lujah!). Three guys covering all that open space behind the linebackers is ringing the dinner bell for a passing team and one with a QB who isn’t Alex Smith or plays for an old school Kubiak offense. Puke.
Since there’s only three, instead of four (or more) DB’s in the backfield, there’s one less safety net. Good offenses will pick that a part like Derek Wolfe feasting on children. The more the NFL has become a passing league, the less teams use this formation as a stable of their defense.
The bad news is, like any zone defense, if the QB can figure out what you are running, he can adjust calls to move the routes into the weaker spots. With Cover 3, one of the weaker spots is the seams that are in between the two outer 1/3rds and the middle 1/3rd.
With that said, against poor offenses or tired and stale ones, Cover 3, with good DB’s can stop the run, set up lots of QB hits and force QBs to throw deep because three yard passes can get you 3 points in a game. It’s a balanced formation meant to handle those duties at once.