See cockfights#8 of 114 things to do in Phuket
For the fight they build a cockpit – a round ring with borders. No one but the referee, the assistant and the fighters themselves are allowed inside the ring; even the birds' owners are ordered out from there. Further, the "golden cockerels" are put head-on, and the fight begins ...
Gamecocks are trained and prepared for fighting since they are chicks. The owners cut their combs, throw them on a diet and buy special equipment (sold in stores) – vitamins, ointments, bandages, trainers and sometimes even blades for their feet, so that the birds can fight off serious injuries. The winning rooster gets into a real chicken paradise – it is surrounded by "hot chicks" for a strong offspring. The loser is left to drag the rest of life alone.
Cockfights take place in bars and villages, but since this "entertainment" is strictly prohibited, its organizers often change locations, so you can find it only after talking with the locals.
By the way, tourists can also send a gamecock to the ring – you can buy a rooster from the locals at a price of several hundred dollars, but without a proper preparation and training the bird cannot survive the fight and can even die.
Editorial opinion: to see cockfights does not mean to hurt your karma, but to bet or participate in any other form in them means to support the cruel treatment of animals.