In the background on the left is the Palace of Fine Arts, and on the right, the St. Francis Yacht Club, one of the oldest clubs on the SF Bay. Between the yachts is one of the Umpire's boats, which follow the yachts closely around the course, watching for fouls, and offering "instant justice" for rules violations. A green flag means you're cool; a red flag means you fouled the other boat, and must perform a penalty, usually a spin, to get even again.