In a 3-4 defense there are 4 backers as opposed to 3. So they have less room to cover compared to the 4-3 where our Mike needs to have good sideline to sideline burst.
This is my take on Saban's big bad 3-4 that talking heads are so enamored with...
Nicky is a bully and his 3-4 is essentially a 5-2 with a tub of lard in the middle to stop up the running game. His OLBs are the same as Chavis' DEs who might drop back to cover guys out of the backfield or just ear up zone space for the short slants, etc.
Nick basically plays a lot of bump and run with his corners while blitzing his basic three down linemen and two OLBs. The blitzes are mixed up easier since he has the four LBs to choose from kinda like when Chavis ran his 3-1 and blitzed with DBs from every possible angle.
The bullying part has to do with the large and sometimes over sized CBs. Saban loves CBs who can play bump and get their opponent receiver late getting into his route so that the QB loses faith in his receivers and starts hearing footsteps from the blitzers. As long as the CB can screw up the route's timing and keep the QB worrying about when his receivers will be breaking free into their routes then that QB will never find any kind of rhythm. At the same time, the CB doesn't have to cover nearly as long or as well as they would playing a little off of the receiver.
The beautiful part about this is that since he is playing with a pretty tight and oversized seven man front, the defense has an advantage against the run built in already.
This scheme has obviously worked very well for the gumps. The only way that any opponent can have a good day against this defense is to force Nick to get away from his bullying mentality. This is usually done with the passing game. It usually takes either a couple of strong receivers to handle the bullying from the CBs or the offense has to spread them out and force them to take out the oversized LBs and put in nickel and dime backs.
Honestly, I think that the only team that has been able to play toe to toe with this defense has been LSU. That is why we hear about "big boy" Football and what not.
This year, however, we have a passing game but do we have two receivers who can handle the bumping CBs? Also, Landry and Odell have been doing certain things that LSU receivers have never done such as those deep back shoulder catches down the sidelines instead of running under the ball in stride. The biggest reason for this year's success is that Mett trusts them to come down with the ball. We have seen how good he looks when things work out. Even forced throws were looking geniousish. Unfortunately, when Landry and Odell do not play at that level the interception probability rises very sharply.
To recap, LSU will have to get Bama out of their oversized 3-4 and make them respect the passing game. Then the rushing attack will work just fine. In fact, with the way that this team is built on the OL and the FB and RB spots, the LSU offense could very well hang just as many points on them as A+M did but again, it will most likely hinge on Odell and Jarvis getting into their routes on time and cleanly.
Also, lets hope that Cam is on his X's and O's because Nicky has become pretty darned good at not only stopping the run but taking away certain things in the passing game at the same time. Cam will have to call the right plays all night long to score more than 40 on these boys.