http://www.footballoutsiders.com/word-m ... ent-918031
If I jog you back to the beginning of the column, you’ll remember I said that Seattle’s secondary was good, but all I’ve talked about so far are their safeties. Their corners are just as important to the two plays I’ve diagrammed as the safeties are, even though neither of them ever show up in the screen.
The reason both safeties are allowed to not only play in the box, but do so while playing the run first, is that both Richard Sherman and Brandon Browner are good enough to play on islands outside the numbers. That means the deep safety just has to worry about the middle of the field, which both of Seattle’s safeties are capable of handling with very little help from the linebackers, so the box safety essentially gets to play like a linebacker.
When you think about great run defense, secondary play isn’t typically the first thing that jumps to mind, but it can be a huge advantage.