The situation you describe falls under Section 5-1f of the USGA Handicap System Manual, 2008-2011. There you will find a list of “Unacceptable Scores” whereby scores made under specific conditions are not to be posted to the player’s scoring record. “(v) When, as a condition of the competition, the maximum number of clubs allowed is less than 14, or types of clubs are limited as, for example, in a competition that allows only iron clubs.” The USGA has determined that a fair test of golf requires a player to use most or all clubs during a round, not exceeding 14 clubs, as per the Rules of Golf. If it becomes a condition of a competition that a player can ONLY use three clubs, or a specific TYPE of club (hickory shafted clubs, for example), this does not meet the standard of a true and fair test of golf ability. You may certainly establish a Handicap Index using fewer than 14 clubs, but when a Tournament Committee sets a condition for a “three club event”, this renders the score unacceptable to your Handicap Index.
Kelly Neely, Sr. Dir., Handicapping & Course Rating