Rule 11 - The Officials: Jurisdiction and Duties
SECTION 2. Responsibilities
The game shall be played under the supervision of four, five, six, seven or eight officials. The game may be played under the supervision of three officials under exceptional circumstances such as injury or delay in travel.
Officiating responsibilities and mechanics are specified in the current edition of the Manual of Football Officiating, published by IAFOA. Officials are responsible for knowing and applying the material in the Manual.
NOTE: The use of mechanics systems that span 3-man to 8-man crews is essential. The use of manuals that only specify a subset of the mechanics is prohibited in international competition. National federations and officiating bodies are encouraged to use standard mechanics in games played under their jurisdiction to facilitate their officials moving between domestic and international games (Exceptions: USA, Canada and Japan).