Just wanted to let you know that I have made some corrections and updates to a few posts. Here is a list of changes:
In the Making Plays post, I've added an explanation of how downs are tracked once a team gets within ten yards of the opponents end zone.
In The Referee and Umpire, I said that the NFL was experimenting with where the umpire is positioned on the field. The League's changes in this regard are actually permanent, and I have added an explanation.
In Timeouts and Coaches' Challenges, I've added a video of an example of "icing the kicker."
I hope these changes clarify the posts, or answered some questions you've had. Also, if you've read The Defense: Linebackers and Defensive Linemen, you should check out the September 5th issue of Sports Illustrated. It has an interesting article about the 4-3 defense and how teams that traditionally use it are changing their defensive formations multiple times during games to confuse offenses.