What is the Cover 3 Defense?

The Cover 3 defense is a defense that relies on three guys to take roughly a third the field, and act as a "safety net" in case the other team gets past the other guys on the field.

What are the origins of the 4-3 Defense?

The most popular form of the Cover 3 defense was created by Pete Carroll with the Seattle Seahawks in the late 2000's

Are there any famous teams who used this defense?

The "Legion of Boom" Seattle Seahawks from the early 2010's utilized this defense, and it was the reason they won the Super Bowl in 2014.