It was a traveler’s trick, of course. The bald joker was himself the Mighty Quinn, king of the gypsy bare-knucklers in the documentary “Knuckle,” a rib-cracking look at the brutal fistfights long used to settle feuds between clans of Irish travelers — nomadic families that go back centuries in Ireland.

“This is always how the families have sorted things out and stopped larger violence,” said Mr. Quinn McDonagh, 44, who heads a clan of about 200 people, mostly in the Dublin area. “Other people use guns and knives to settle things — we do it through our fists.”

He had cut loose the publicist who coordinated the interview and ordered up pints of beer, so that a proper discussion could be conducted here in this Irish bar in Hell’s Kitchen.

Next to him, Mr. Palmer, who made “Knuckle,” looked as if he knew the drill. After all, he had hung around with Mr. Quinn McDonagh for 12 years to make the film, which opens in select theaters in New York City and Los Angeles on Dec. 9 after an impressive run at festivals, including Sundance, Hot Docs in Toronto, and Irish Film New York (where it was named best film last month). HBO has even aquired the rights to make a series based on the film.

This is hardly the first star turn for traveler culture. The 2007 cable series “The Riches” featured Eddie Izzard and Minnie Driver as the leaders of a con-artist traveler family in the United States. “My Big Fat Gypsy Wedding,” a British reality series that began last year, chronicles over-the-top nuptials there. And who can forget Mickey O’Neil, the Irish traveler bare-knuckle boxer played by Brad Pitt in Guy Ritchie’s 2000 film “Snatch”?

“Knuckle” is fueled by the personality of this big man, who is undefeated in fighting for his family name against the Joyce and Nevin clans.

Never mind that the three clans themselves are interrelated with, as the film puts it, “brothers and cousins fighting brothers and cousins.” One family member in “Knuckle” points to the absurdity of the self-perpetuating feuds and fights: “At least wars are about something.”

The feud in the film was supposedly started by a torched tinker’s cart at a horse fair, and renewed in 1992 by a deadly fight outside a pub, for which Mr. Quinn McDonagh’s brother Patty served prison time for manslaughter.

In the film, Mr. Quinn McDonagh is derided as Baldy James by rival clan members who send taunting videotaped challenges, a modern wrinkle on this centuries-old tradition.

“The fights help settle a score, but then the next tape arrives and everyone gets stirred up again,” Mr. Quinn McDonagh said in the interview.

As a referee scolds two boxers in the film, “It’s what you say on the videos that keeps the fights going.”

As it happened, videotape helped open the door for Mr. Palmer. In 1997, he videotaped a Quinn McDonagh wedding and the family then invited him to shoot Mr. Quinn McDonagh fighting a Joyce. Mr. Palmer followed a triumphant Mr. Quinn McDonagh, 20,000 Irish pounds in his bloody hand from side wagers, rushing back to “a giant fan gathering” at a pub in Dundalk, Mr. Palmer recalled.

“It was like a medieval knight coming back from a tournament,” Mr. Palmer said. “An amazing, huge world had just opened up to me, the most amazing thing I’ve ever had the chance to film. I remember calling a friend and saying, ‘I really have to find a way to make a film about this.’ ”

He did find it, by hanging around the feuding families for the next decade. It started as a bit of a tradeoff, he said, with the Quinn McDonaghs giving him access to the fights and Mr. Palmer giving them some footage. The travelers had already been taping their own fights and either selling the footage in streets and pubs, or editing it into “threat tapes.” “In a way, they were already documenting themselves,” the director said.

Mr. Palmer grew up middle class and well educated in the Dublin suburbs and like many Irish “settled” people, he knew travelers from seeing them solicit work at the door, women asking for old clothes to mend and sell, and men offering their tinsmithing skills to fix garden tools and sharpen knives.