Amtgard is a major fantasy boffer larp in the United States. It uses the common American convention of “chapters”. Chapters are clubs that agree to all play by the same rules. This allows Amtgard to federate itself over a large area. The result is that you’ll find this system all over the USA and also in other continents. For example continental Europe.
The Larp Rule Books
As an organisation, it has developed considerable support for its members. This includes the rulebooks referenced via this post. In fact, it has its own library of books.
The link here not only gives access to the main rulebook. but also supporting monster rules. Additionally, there is support for chapters as well.
However, if you need more information; it exists. There is a Wiki. And a rules discussion/clarification group on Facebook.