how to read a defense

Question
My question really may not be actually 1 question. I'm trying to get an understanding of how a QB reads a defense in a passing situation. I've heard the term "progression" used as something the QB needs to do when he reads the defense. Exactly what is progression?

My second question may be directly tied to my first one, and I hope its not too general. I do know that if a WR goes in motion and the CB follows, that is an indication of man coverage. When the CB does not follow that is a zone defense. How do the safeties and LBs react in man and zone coverages? Do they tend to backpeddle, or run at their man? Quarterbacks have very little time to make a decision on who and where to pass the ball. I'm trying to educate myself on what the QB is supposed to "see" and "read" that will in turn make them throw the ball to the proper receiver.

I eagerly await your reply on this. Thank you for being available to answer these questions.  

Answer
Dear JP,
Being able to read a defense is not hard. All you have to do is take the time to break down the defense into groups and sub-groups.

By the time a quarterback takes the field, he must know the coverages that his opponenent is going to run against him.

He must ask himself, what do they like to run on first down?, second down?, third down?, do they play run on the first two downs?..... Also read the corners backs.

Corners backs, are the quarterback's best friends, when it comes to giving the most tips to the coverage. Here are a few simple reads for the quarterback; Study the corner back, look to see if he his eyeing the receiver or quarterback.

If he is eyeing the receiver he is in some type of man coverage.
If he is eyeing the quarterback he is a zone coverage.
If he is line-up outside the receiver he is in a zone coverage.
If he is line-up inside the receiver he is in a man coverage.
If he is line-up in a low focus position he is in a man coverage.
If he is standing tall he is in a zone coverage.
IF HE IS LINE-UP INSIDE AND LOOKING IN TO THE LINE OF SCRIMMAGE HE IS COMING ON SOME KIND OF STUNT. Make sure you have someone pick him up or he is going to hand you, your head.

I hope this will be of some help to you. The only book that I know that talks about reading the defense is,

"Winning Football with the Air Option Passing Game"
by Homer Rice & Steve Moore.

This is one of the best books out today. I have a copy.

Your friend, coach Louis