www.paradisebymarriott.com/feeds/vacation.php?include=135441 In a nutshell, it was a religious rite performed to deliver a message to the god of fertility. Later, it was camouflaged as sport so that the Spaniards would not punish the participants or banish the practice.
With each revolution around the pole, the rope would feed out and the upside down twirlers would be lower to the ground by another few feet. The gentleman at the top of the pole would beat his drum and blow his flute as the twirlers descended. Very puzzling if you didn't know the reason. When they reached the beach, they stood around for awhile, I imagine to get rid of any dizziness, then they climbed the pole, retracted their ropes, and did it again. Amazing.