RedactedNarrative: Operator of vessel #2 stated he was involved in a race event at the Yacht Club when he was struck port side by vessel #2.  Vessel #1 stated he was going to take vessel #1 on his stern when shifting from one helm wheel to the other he slipped on the boats deck and fell down.  He lost control and collided with vessel #2.  Even though operator of vessel #1 fell he was still in violation of Rule 12 of the CG Navigation Rules.  No injuries.