Cover 3

After watching this weekends NFL playoffs I decided to write an entry about Cover 3. I picked Cover 3 because I think it's the best way to get into an 8 man front and still play good zone pass defense. There are other ways to accomplish both of these tasks but I like Cover 3 because I can use almost the same coverage rules for my corners and middle of the field safety that I will use in my zone blitz packages. It makes teaching my defensive package that much easier.

Against the standard 2 RB, 1 TE set (21 Personnel), there are 7 potential blockers on offense if the QB is not a running threat. There are 5 offensive lineman, 1 TE, and 1 FB. If the defense aligns in a 2-deep shell there are only 7 defenders present in the box to immediately stop a running play. This means that each defender is accounted for, with nobody free to tackle the running back until he's gained significant yardage. This is the basic math used by quarterbacks and offensive coordinators alike to determine when easy yardage can be gained by checking into a run play.

By rolling one of my safeties down into the box, and moving the other safety into the middle of the field, I get a 1 man advantage in the box to stop the run, and I position a player right into the middle of the field, which, if you're going to be a good defense, you must defend.

Below is the pre-snap alignment for Cover 3, also referred to as '3 Sky'. The 'Sky' designation tells the defense which player is responsible to be the 'force' player versus a running play, and the 'curl-flat' defender versus a pass play. In this case, that player would be the safety.We'll go over the other 2 versions of the call later.

Against a running play, the safety rolled down into the box will be responsible for maintaining outside leverage on the ball carrier. By maintaining outside leverage he 'forces' the ball back towards the inside, where 10 other defenders are pursuing from. If he fails to 'force' the ball carrier back inside, the back is in a footrace to gain as much yardage as possible before being caught or scoring. In either case, we've given up a big play and that's unacceptable.

This picture represents the basic pass coverage responsibilities of the '3 Sky' call. In my next post we'll very thoroughly cover the concept of Pattern Matching and how each defenders coverage responsibilities can and will change once the eligible receivers have begun to run their routes.

You'll also notice in the above picture that the 4th pass rusher has become the Sam backer instead of the Rush backer. This occurs because somebody has to be responsible to be the 'force' player against the run and the 'curl-flat' defender against the pass on the weak side of the formation as well. If the Rush backer were rushing the passer, this responsibility would fall to the Will backer. Unfortunately, the Will backer, by his alignment, is in terrible position to gain outside leverage on a running back intent on getting to the outside. Giving him this responsibility would be setting him up for failure and we would be constantly gashed by big plays. To fix this, we simply give the Sam backer the job of rushing the passer and the Rush backer the job of 'setting the edge' against the run and being the 'curl-flat' defender against the pass. This assures that our call is schematically sound and cannot instantly be taken advantage of by a simple outside running play to the weak side.

This picture above is the basic alignment for '3 Backer' coverage. You'll notice that our safety who has rolled into the box no longer has the outside leverage he had in the '3 Sky' call. He is lined up in a traditional linebacker spot. This is because the Sam backer is now the 'force' and 'curl-flat' player to the strong side. It is his responsibility to 'set the edge' on running plays to his side, forcing the ball carrier inside of him, to where his help is. This also prevents him from rushing the passer, which could be a good thing. Now your primary pass rushing player gets to rush the passer. This alignment also moves the Will backer into much better position to gain outside leverage on an outside running play to his side. The basic coverage assignments are shown in the picture below.

The third and final version of Cover 3 is '3 Cloud'. This is a call that you don't see very often, but it can represent a nice change-up of assignments if you're a defense that plays a lot of Cover 3 and the offense is calling plays designed to take advantage of it's weaknesses as a coverage.

You'll notice that in this diagram, the ball is on the right hash and not in the middle of the field. This is generally the only time you'll see '3 Cloud' called, because as you might be able to guess, the 'Cloud' designation means that the corner is responsible to be the 'force' and 'curl-flat' defender. This assignment can become impossible unless we dictate that the corner with these responsibilities is the one on the short side of the field, the boundary corner. The corner on the other side, the field corner, is too far away from the action, and can too easily be sealed off by a good block from the WR to execute this assignment correctly. You might also notice that the Will backer is the same alignment he would be for the '3 Sky' call. This again means that the Rush backer must be responsible for this assignment, also requiring that the Sam backer be the 4th rusher in our pass rush.

 In my next post, I'll go over in detail how the pattern matching coverage behind Cover 3 really works. We will really get into the nuts and bolts of the coverage. But for now hopefully you have a better understanding of exactly what Cover 3 is. It's a great call when you need to stop the run but don't want to get into a man for man coverage. It's also a popular 'junk' call, meaning that if a defensive play caller gets stuck in a certain situation and isn't sure what to call, he can call Cover 3. It adjusts well to multiple different formations, gets an extra guy in the box to stop the run, and defends the deep middle of the field. We'll go into much great detail next time.