THAT PHANOM, Thailand — Sprawled on a bamboo mat, Supattra Inthirat closed her eyes as her father massaged her hard arms with oil and menthol. In preparation for her 15th muay Thai bout, her father whispered a prayer into her ear.

When Supattra, a 12-year-old fighter known as Pancake, faced her rival and 400 fans under halogen lights, she would be fighting for a purpose: $60, almost a half of a month’s salary for Thai families in this region.

“She will be a champion,” he said. “She must train early to build up her boxing bones.”

Across Thailand, muay Thai is a hallowed style of kickboxing propelled by both rich and poor. For the poor, it can be a form of social mobility, a means for muscled young boxers to fight their families’ way into the burgeoning middle class. For the rich, it’s a brutal gambling form in which tens of thousands of dollars can be won and lost each night.