I just want to call BS on the whole 4-3 argument, because the posts I have read lately have inferred that it's a better formation than the 3-4. As if the number of players that put their hand in the dirt makes a difference.
Ok....
I can't draw out a diagram of Xs and Os on this thread so you'll have to use the chalkboard in your brain.
When you have 4 down lineman, there's 5 guys that can block them up front. That means 1 on 1 with 1 olineman free.
Now, if you've got a monster at nose (Casey Hampton, Vince Wolfork etc) then your center AND guard HAVE to double him. That leaves 2 tackles and a guard. The guard takes your DT, and the tackles have your 2 DEs.
So you have 3-- 1 on 1 match ups AT the line of scrimmage. 3 chances to get 1 winning match up. 3 guys have a shot to getting to the QB. You just need 1 to get free.
If you rush 3-- it's 3 on 5.
You can double the best 2 and still have a free lineman to block the 3rd. If you bring a LB on a blitz, he's coming in NOT from the LOS-- nope, he's 3-4 yards away when he blitzes. That plenty of time for one OLineman to come off his double team and pick up the LB. And your 3 Dlineman have already been slowed down just enough that when that LB comes, the OL guy leaving his double team simply needs to get a piece of that LBer to give the QB that half second he needs to get the pass off.
Realize, from the moment the ball is snapped you've got 3.5 seconds to get to the QB. That's it.
The farther you are from the QB when the ball is snapped (LBer) the longer it takes to cover that distance-- AND the more warning the blocking OL has. A blitz has to be timed PERFECTLY to work.
So lets say you cheat the blitzing LB up--- OL is going to see that, alert each other with calls, the QB is going to hear that and adjust the play call. Now you're blitz is fvcked before it ever starts.
Let's say you bring two LBers up to the line to blitz with a 3 man D front--
OL checks down to a "max protect" front and goes "cheek to cheek" and the QB gets the snap and IMMEDIATELY throws to his "bail out" receiver (it's called "hitting the hot route") which is usually just a quick slant for 2-3 yards.
Now if you gave me Vince Wolfork, JJ Watt and Bruce Smith in their prime, I'll run a 3 man front ALL DAY-- and I'll have you playing your 4th string QB by halftime because I'll be forcing you to double team all 3 of those guys with 5 lineman AND your TE. At that point, you're fvcked. One less receiver running a route (TE) which means I've got a FREE LB that I can blitz from where ever the fvck I want and you'll never be able to stop me.
But we don't HAVE 3 guys like that.
So that's why we need 4 down Dlineman.