Before I get into the quarterback position, it is a must to delve into the wide receiver position.
A quarterback will have from 2 to 5 options on every given play. Everyone knows that a quarterback has his go to receiver and he is usually primary option number 1. That option isn't necessarily the fastest receiver or the one with the best hands. It is most often the one that runs the cleanest route.
Does he run the route at the exact same speed? Does he round off the route or flow through cleanly. Does he recognize the soft part of the coverage by thinking of where the quarterback will see the opening?
It is all about timing with your target. Marvin Harrison is the standard. How often do you see Peyton Manning looking left, he turns his body and fires to the right side hitting Harrison coming across on the quick slant seemingly with no more than a glance. All of this happens within 3-4 seconds.
It doesn't take longer because Peyton knows exactly where Marvin is going to be. Marvin runs that middle slant at the same speed every time. He is running to a certain spot on that pattern every single time. This allows the trust to develop between quarterback and receiver.
Now to set up that slant over the middle Peyton is looking down the middle of the field and will then give a look left to pull the safety to that side of the field. He will roll his shoulder just a bit to sell it or he will use the pump fake but it forces the safety to take that step to the left and when he does make the throw the safety does not have time to change momentum and recover.
So while the quarterback is dropping back into his 5 step, he may be eyeballing the receiver wide left but that receiver is not the primary option.
If the safety stays put, the quarterback has scanned the middle and looked left, so options to that left side and middle are know a known commodity. If nothing is open to that side and the safety has stayed at home, the quarterback then looks for the quick dump down option. This is often the tight end or running back.
If they are covered the ball should be sailed out of bounds.
Now to get through the progression and throw several things must have occurred.
The quarterback must make an intelligent pre-snap read. He has to figure out what package the defense is in and where the blitz is coming from. He must also look at who his receivers are matched up against. Do they have a slow linebacker in 1 on 1 coverage, against the tight end? Is coverage loaded to one side?
This is where the audible comes into play. Recognize the defense and make the right adjustment. Deep cover 2, throw underneath and allow the receiver to make the run after catch. Wide zone, the middle is open. Man coverage with 7 or 8 in the box and you take your chance deep with the one on one coverage.
To get from that initial pre-snap read to the throw is also a process. The quarterback must make his final decision as he is dropping back whether it is the quick 3 step drop or the slower 5 and 7 step drops.
Once his back foot plants he should be ready to make his decision on where the ball is going. If he hasn't then he is dependent upon the line to give him added time to make the read and throw.
Making the throw is pure mechanics for most quarterbacks. There are the free lancers that seem to be able to will the ball to the receiver but those are rare.
First is getting the right grip on the football. This is why you see the quarterback before a game practicing just holding the football out to his side.
As the quarterback drops back, you like to see the ball in high at the top of his numbers. His head should be squared to his shoulder and his eyes focused down the middle of the field. His forearms should be loose against his sides but not wide of his body. Holding the ball low at the waist is a strip of the ball waiting to happen and it also adds another half second to the throwing motion.
Drawing the ball back should be the top half of a circle. While cocking the wrist gives the quarterback the zip on the ball. You like to see the ball come back just past the ear with the elbow at a 90 degree angle. The quarterback's elbow should be almost like a gun site aimed at the intended target. Palm should be out and thumb low.
As he uncoils his throw, the ball should be release at the top of the throwing motion. Too early and the ball sails. Too late and it hits the dirt. The follow through should carry through from shoulder to shoulder.
Feet are just as important as the upper body when throwing the ball successfully. Feet are like the eyes they should be moving and adjusting. The accuracy comes from the front foot. Just like the elbow, the front toe should be a site to the receiver. The back foot is your power and follow through.
The hips should be open and not tight. The knees should have a slight bend and not locked. Locked knees will lead to injury. This is the process that allows the weight transfer from the back foot to the front foot as the pass is being made.