Learning more about technique and play strategy.

I love to read and I love football. I was wondering if anyone knew of some site or book that does a good job of discussing defenses, offensive schemes, or technique for the players. I just would love to be more informed when I watch. It would be fun to be able to watch the pre-season games and be able to critique people who are far more talented than me on their footwork. Or it would be fun to be able to analyze play-calling beyond just what seems right to me.