The cover 3 zone is a very standard defensive scheme for the secondary and linebackers. As the name would imply, the cover 3 zone deploys three deep defensive backs to cover their respective 1/3 of the field (see figure). The basic philosophy behind the cover 3, is to provide a good balance of run and pass defenders. Providing more deep defenders than the cover 2, this defensive scheme makes it more difficult for passing teams to come up with big plays down the field.
Who Plays What In a Cover 3 Zone?
Typical assignments are as follows.
The three deep zones in the cover 3 are most often covered by the two cornerbacks (left and right 1/3), and the free safety (middle 1/3). The strong safety will have curl/flat responsibility on the strong side, and the "Will" linebacker will have the weak side flat/curl zone (How to determine which side is weak and which is strong).
What Are the Strengths and Weaknesses of the Cover 3 Zone?
This scheme has some great strengths, including a balanced run/pass defensive philosophy. There are 3 deep defenders, which means less ground to cover for those defenders, as compared to a cover 2. If your defensive line is strong and your players are disciplined, you can make the cover 3 a standard tool in your defensive toolbox.
The short routes become a little vulnerable with the corners bailing to get deep in their zones. While it provides balance between the run and the pass, it also is not particularly strong in either area. Good offensive schemes will be able to recognize the cover 3, and will have pre-set audibles designed to capitalize on these weaknesses. If you are facing a strong running team, the cover 3 is going to be less than ideal, unless you have some great strength in the trenches.
If you have good balance on your team between your defensive line, and your linebackers and secondary, the cover 3 is a solid scheme that can work well against both the run and pass. It's a standard scheme used by many high school, college and NFL teams.