What's really needed for a good defense?

[Vince148]

I was looking at some "game films" and pictures, and I notice a lot of defenses are just lined up straight across the LOS with maybe a safety playing back 10 yards or so.

As I experiment with different defensive formations, it doesn't really appear that it makes a whole lot of difference whether I'm in a recognizeable formation or not. Sometimes, I'll play with a fairly distinguishable 4-3 and other times, I'm using 4 loopers coming off the ends while manning up with my DBs and maybe playing a LB or two in the interior.

Either way, the results seem equally the same.

So, if I'm on defense, what do I really care about? What do I want to accomplish? I basically have two defenses, a run stopping defense and a pass stopping defense.

Why are some of you using 9 men on the LOS? What are some of your basic defensive ideas?