I had the pleasure of listening to Tosh Lupoi, Defensive Line Coach at the University of Washington, speak at a Glazier Clinic earlier this year.
His presentaton was impressive. He really changed my mindset for how to mentally prepare defensive linemen on every snap.
He puts his guys into three different modes depending on what they are trying to accomplish. Stances, alignments and the thought process changes in each mode.
Whenever the defensive linemen aren't expecting to rush the passer and they are not stunting, they are in base mode. Their stance must be balanced and powerful in order to react to the different types of blocks they see.
They should have their eyes on the blocker they are reacting to and their hand off their leg. If they happen to rush the passer out of base mode and they get engaged by an offensive lineman, they should attempt to use a push/pull move or long-arm (basically a violent punch that separates them from the offensive lineman) the blocker.
Lupoi didn't go much into what they do exactly in stunt mode due to time restrictions, but I would assume the stance would complement where they plan on moving towards without giving away where they are going. The stance doesn't need to be as balanced as in base mode and the defensive linemen should have a pre-determined plan for how they are going to attack the gap they are stunting to. Their eyes should be on the ball.
This is the mode defensive linemen need to get into for a pass rush emphasis. They should transition from a balanced stance to a speed or sprinter's stance with narrow feet, butt up in the air, head down and looking inside towards the ball. I have seen guys (most recently the Philadelphia Eagles' Jason Babin and Trent Cole and their notorious Wide 9 alignment) use a four-point stance when they are in this mode, but I would suggest doing whatever is most comfortable for you as a coach. I don't know which one was is better for this mode, but I'd be willing to let my players decide what is most comfortable for them.
Lupoi wants his guys to have great takeoff, so he emphasizes rolling and leaning out of their stance. It's the exact reason, the NFL makes guys come to a pause in their stance for one second before taking off when they time 40s at the combine.
In order to accomplish this though, they must understand the opponent's cadence. The DL should use a credit card alignment (you shouldn't be able to slip anything more than a credit card between the DL's head/hand then a credit card), loosen their width on alignment and get into a gap alignment instead of on a shade. When they takeoff out of their stance, the DL should replace their hand with their foot on their first step.
Mentally, the DL needs to have a plan. Their goal in Lupoi's mind is to effect the passer. They should have a move they want to attack the OL with and a counter in case it doesn't work.
In the end, Lupoi wants to coach violent, aggressive pursuit over anything else. While he teaches his guys "rush lanes", he preached not to over coach it while emphasizing that most QB scrambles through the interior first, not on the edge.
Making it Happen
You can tell your players you are going to use different modes, but unless you have a way to communicate this to them during the heat of battle, it's not going to matter much.
First, these modes should be drilled in practice. This needs to happen in individual periods first and then can transition into team periods later.
We will always be in base mode unless the DL has a stunt on, in which, surprise, they will be in Stunt mode!
You can have your players get into Jet Mode in one of three ways.
1. Yell a call out to them from the sideline
2. Have a player identify down and distance every play (this means you must teach your players what D&D you want them to be in Jet mode in)
3. Send in a Jet package (my preferred method), where you will have your four best pass rushing defensive linemen in the game regardless of size. You will only use this in obvious passing situations though. So, it's critical you know your opponent's run/pass tendencies based on D&D.
Some of you may have a hard enough time getting your freshmen DL into a normal 3-point stance, so I wouldn't suggest using this at lower levels. More advanced Varsity DL will be able to handle this transition though. If nothing else, create a pass rushing mentality and let your DL loose on obvious passing situations.