I am starting to work a semi-pro league this weekend where they use NFL rules. Anyone know where to find a quick reference of the rule differences?

There are an absolute ton of them. Email me personally and I'll send you a bunch of stuff I have that will help you. This is my school email address. I am the R, and if you are the R, you REALLY will have your work cut out for you.
[email protected]

My friend, you don't need a rule book, you need boxing gloves and full body armour. I've done it, and it 'ain't' fun at all. Make sure you get paid first.
Good luck

booker227, I have to disagree with you. My experience with semi-pro football has been most rewarding. I have officiated semi-pro football for 18 years. I work 10-12 regular season games plus play-offs. I work all the home games for teams in two leagues. I have worked 3 league championship games, 10 quarter-final or semi-final games, 3 all-star games and a bowl game in one of the leagues. I quit officiating college when the semi-pro opportunity came along. No travel except for playoffs. This past June I was inducted into the American Football Association Hall of Fame. The AFA is a nationwide semi-pro organization. Yes, it is a lot of fun.