Here's indieWIRE's interview. The synopsis is below, courtesy of Sundance:
Residing in Ireland and parts of the United Kingdom, the Travellers are a traditionally nomadic ethnic group with their own customs and a deep sense of clan pride, despite being interrelated by marriage within their small population. When conflicts arise, arguments are often settled through ritualized, bare-knuckle fighting. Director Ian Palmer followed members of the Traveller community for 12 years and became privy to a decades-long family feud of Hatfield-McCoy proportions. At the center of the conflict is James, the confident, yet reluctant, defender of the Quinn McDonaghs, who is frequently challenged to fight his cousins, the Joyces. An outsider in a secretive world, Palmer waited years before he began to learn the reasons for the animosity between the rival clans. Disturbingly raw, yet compulsively engaging, "KNUCKLE" offers candid access to a rarely seen, brutal world where a cycle of bloody violence seems destined to continue unabated.