Defensive formation

Question
Can you e-mail me how to do pre-snap reads of defensive formations and how to adjust to them?

Answer
Shawn, are you asking this as QB, a skill position player, a coordinator or a fan?

I will give a short, basic response, but I would like to hear the context for your question:

Every football play is a tactical guessing game.  The defense is trying to guess what the offense will run - a pass play or a run play, a deep play or a short play, because they will skew or stack their defense to try and gain a situational advantage for that play.

 Let's say you are sure the offense will try a running play.  You have some kind of deep zone cover scheme and cheat the strong safety up towards the line of scrimmage and "put eight men in the box."  That extra man in the running box makes it likely you will stop the running play.

 But if you have a savvy QB like Tom Brady or Peyton Manning, he may notice that safety cheat, make a change to the play at the line of scrimmage (an audible), and throw a pass.  The pre-snap read allows the offense to react to the defense's guess, and suddenly the offense has the situational advantage ?the defense is ready for a run, and when the offense runs the audibled pass play, they have a mis-match.  There should be a man open to throw to.

That is an example of the kind of things a QB or coordinator will do before the snap.