This isn't everything about pass defense but it's a start. The blog article is here: http://codeandfootball.wordpress.com/2013/07/04/from-cover-0-to-cover-4-in-images/ Cover Zero Cover zero implies everyone has a man to man assignment and there is no free safety. Good for blitzes. Bad if your opponent is named Bob Hayes. Front in use is the Tampa Under. Man Free "One free" or "man free" was called by Dr Z the purest form of man to man. If you're a great cover safety, you might double the most dangerous man on the field, or if you're Larry Wilson, maybe you just safety blitz every so often. The front is the Miami 4-3 (4-3 slide, 4-3 stack, etc). Cover 1 Mostly man-to-man, but with guaranteed deep help from a safety. Miami 43 shade front. Cover 2 If you have ever heard of the phrase "double zone", then Cover 2 is the original double zone. There are resources that say that the 1963 Bears used a double zone and confused everyone in their day (people back then only used rotating zones, if that). Important in the Cover and Tampa 2 are the jam by the corners up front. It slows the receivers. If you have a fast, agile middle linebacker, the defense invented by Bud Carson and named after Tony Dungy's Tampa Bay Buccaneers offers better deep protection down the middle. Tampa 2 Tampa 2 with a Tampa under 4-3 front. Cover 3, rotating and modern. Back in the days of the Vince Lombardi sweep, this was simply called "zone defense". In the modern context, it's a rotating zone with a Cover 3 back end. It was good for blanketing one good receiver. The Baltimore Colts were good at this. Joe Namath was good at diagnosing it. Joe sent Don Maynard deep early in SB III, and the Colts conveniently rotated towards Don. That, I suggest, was a mistake. The front in this example is Tom Landry's original 4-3, a 4-3 inside/outside. The ease with which the rotating zone was diagnosed led to it disappearing. The modern Cover 3 is often associated with three deep defensive backs, and 3 Dbs are often seen with that is called the overshifted secondary. One safety will fall to linebacker depth. This safety is often called a monster or rover back (If you've ever heard the phrase 5-2 monster, this is where it comes from). The front here is the 4-3 Stack (i.e. Miami 4-3), with a safety at linebacker depth (a 4-4 setup). This is a favorite of Ron Vanderlinden, a coach who was the defensive coordinator at Penn State. QQH coverage (quarters - quarters - half) Another look with 3 defensive backs is quarters - quarters - half coverage. You can use this to crowd a team that is flooding one side of the field. Because it is also suitable for use with a 3 deep backfield, we show it out of the overshifted 4-3 Stack. Cover 4 A kind of prevent, shown from a Tampa under front.