MONTREAL — It is one of sport’s biggest mysteries: how did hockey come to tolerate fighting? Hockey historians say that no one knows why or even exactly when the game decided long ago to tolerate fighting while other violent-collision sports like rugby and football did not.

But Adam Gopnik, a writer for The New Yorker, has offered a theory that tries to explain why fighting and violence seem to be in hockey’s DNA. He regards violence as an outgrowth of organized hockey’s origins in late-19th-century Montreal, where ethnic groups formed rival clubs that gave the game the “archaic tang,” as he put it, “of my gang here versus your gang there.”

Gopnik, who grew up here and is a Canadiens fan, sees hockey as the most creative sport, but also “the most clannish, most given to brutal tribal rules of insult and retribution.” For him, the key lies in the fleur-de-lis, the rose, the shamrock and the thistle that adorn this city’s flag.

Gopnik offered his hypothesis last November at Canada’s biggest annual intellectual event, the Massey Lectures, which since 1961 have featured speakers like Dr. Martin Luther King Jr. and Margaret Atwood. It is also contained in a book based on his lectures, “Winter: Five Windows on a Season.”