If you like football and you're also a nerd...

Check out Advanced NFL Stats.

On a related note, I tried reading The Hidden Game of Football once. It was pretty interesting, but I couldn't finish it because the attempts at humor were really grating. For all the alternative methods of measuring statistical success that were laid out in the book, the only one that stuck with me was an early mention of what constitutes a successful play. Basically, (as I recall) on first down a minimum gain of 40% of the distance remaining (so, four yards on a first and ten), 60% of remaining on second down, and 100% on third or fourth down were positive plays. Pretty logical, but it has changed, albeit subtly, the way I've watched football*.

* The last time something I read changed the way I watched the game was from either an interview with or from One Knee Equals Two Feet by John Madden where he advocates focusing on the offensive line at the snap. Before, I tended to watch the quarterback, but the movement of the line will tell you the nature (pass or run) and direction of the play well before whatever the quarterback does.