Reading Defenses

Question
Victor,
I know this is a complex question, however I was wondering if you could explain to me how a QB reads a defense.  What are the various different coverages?  How does a qb know which is which from a pre-snap read?  What's the best way to attack the various defenses?  Thank you very much.
David

Answer
David
This is a complex question that cannot be answered completely in a written answer, but I am attaching some excellent links to help you reading keys.  These links are to instructional video clips that are by experts themselves.

Watching safety http://www.youtube.com/watch?v=5kS5lh63LNo

http://www.youtube.com/watch?v=mn4eQvkqArg

http://www.youtube.com/watch?v=_Kb5XVCEI78&feature=related

http://www.youtube.com/watch?v=p4iibdx90ak&feature=related

Cover 2 Man http://www.youtube.com/watch?v=irNYNOtJUFU&feature=PlayList&p=4E0084F8EAC5E9EA&i...

Pass Routes  http://www.youtube.com/watch?v=b2k59617MJs&feature=PlayList&p=34409BA9C78BB365&p...

Reading  http://www.youtube.com/watch?v=6XT8e6zlY-g&feature=PlayList&p=02180BCFDA0562EC&p...