Here is an article I wrote for my site about this.
http://www.footballrefs.com/show_article.php?id=1
BTW, Bob M has written an extensive article covering many more details of penalty enforcement and it is an OUTSTANDING document.
http://www.footballrefs.com/show_article.php?id=3
FYI:
Both articles are from 2003. There were some minor changes to Post Scrimmage Kick enforcement this year that need to be changed in each article. Bob has made his changes but I have yet to post them. I haven't yet made the changes to mine (to my shame)
[Edited by mikesears on Aug 11th, 2004 at 07:42 AM]