This is one of those passages where you go from “duh, of course” to “damn, that makes sense”:
I really, truly believe that for a person implementing a 3-4 scheme, choosing the coverage first is crucial. The 3-4 has a lot of moving parts, more so than just about any other defense, and often has changing responsibilities with regards to force, contain, spill, all those terms we love to use to define good defense. The difference between the 3-4 and other defenses, in my experience, is that the 3-4 has the interesting feature that the front and the coverage are intertwined. If you want to run a certain coverage, you need to do certain things with your front. There is a minor assumption that is working behind all of this: you want to rush at least 4. If you don’t mind rushing 3 and dropping 8, well, no biggie. But if you’re going to rush 4 in the 3-4, you need to marry the front and the coverage. You have to make a conscious decision about what you’re doing.
There’s a lot more there to chew on. Definitely worth a read if you’re trying to get a handle on what Grantham is up to.
(h/t Smart Football)