Asian elephants can weigh more than five tonnes (11,000 lb)and move at more than 25 km (15 miles) an hour.
Mahouts handle the elephants while the players try to strike the ball with a stick that is much longer than the one used when playing on a pony. The ball is the same size as a regular polo ball.
"A lot of my experience lately has been rodeo," said Canadian Adam Janikowski, one of the players. "I don’t think I ever want to do rodeo events with any of the elephants."
Elephant polo divides conservationists.
Some say it is cruel. Others say it has helped to raise funds to protect the animals and has highlighted the problems they face through habitat loss, poaching and abuse.
Organizers said the King's Cup has raised more than $1.3 million over 15 years.
The elephants are treated to a buffet of fruits and vegetables.
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