[SmootSmack]

I think Joe Crisp did a really good job of explaining the gap defense a few weeks back in another thread, one of the best I've ever read actually. So I'm just going to repost what he wrote:

"When coaches explain to their D-linemen where exactly they want them to line up on a given play, they use a numbering system based on the O-linemen and the gaps between the O-linemen.

Using the Center position on the offensive line as the starting point, the Center is "0", the gap between the center and offensive guard is "1," the offensive guard himself is "2," the gap between the offensive guard and offensive tackle is "3," the offensive tackle himself is "4," the gap between the offensive tackle and tight end is "5," and the TE himself is "6". The TE's inside shoulder (or "shade-in") is "7," the gap fully outside the TE is "8," and the TE's outside shoulder (or "shade-out") is "9." It looks something like this:

.....TE...OT...OG...C...OG...OT...TE

8.....6....4......2....0....2.....4......6.....8

....9..7.5....3....1.....1.....3....5.7....9

So when I describe Jermaine Haley as a more ideal "0" or "1" gap player, I mean he is best suited for playing heads-up on the Center, or in the gap between the center and guard (this gap is also referred to as the "A" gap). This is because you generally want a heftier, "roadblock" type of DT in there as an anchor who can occupy two blockers (generally the center and a guard) without getting run-over. A successful "0" or "1" technician will divert blockers from the linebackers and other D-linemen, and make it easier for the linebackers to diagnose and attack the play.

Cornelius Griffin and Joe Salave'a, on the other hand, seem better suited for playing "2" or "3" techniques, where they will try to shoot the gaps between the OG and OT. Often, they attack the vacancy left when a guard double teams the "1" technician with the center, or when an OG double teams a DE with an OT. They are generally quicker and more agile than "1" technicians, but rely on the anchoring effect of the bigger DT to burst through the gaps and into the backfield."

Thanks again to Joe Crisp for that clear, concise explanation of gap defenses.