Excerpts from the Official Rules of Ultimate: 11th Edition
From the Preface:
“The integrity of Ultimate depends on each player’s responsibility to uphold the Spirit of the Game, and this responsibility should remain paramount.”
From Section 1. Introduction, item B.
“Spirit of the Game. Ultimate relies upon a spirit of sportsmanship that places the responsibility for fair play on the player. Highly competitive play is encouraged, but never at the expense of mutual respect among competitors, adherence to the agreed upon rules, or the basic joy of play. Protection of these vital elements serves to eliminate unsportsmanlike conduct from the Ultimate field. Such actions as taunting opposing players, dangerous aggression, belligerent intimidation, intentional infractions, or other ‘win-at-all-costs’ behavior are contrary to the Spirit of the Game and must be avoided by all players.”
For more information: http://www.usaultimate.org/about/ultimate/spirit_of_the_game.aspx