What books/articles/other stuff would you recommend reading or doing in order to better understand the theoretical concepts of football (the x’s and o’s level)?

For books Pat Kirwan’s Take Your Eye Off The Ball is a great place to start. You can also dig through the archives of SmartFootball.com. There’s a wealth of Pats-specific information in there. Chris Brown also wrote The Essential Smart Football, which is a collection of his best articles. Here’s one of his best Pats articles, Ode to the War Daddies.

Blood, Sweat and Chalk is another one I enjoyed that touches on the evolution of schemes in football. There are plenty of more specific books, but those are some good places to start.