tl;dr It's complicated.

The story begins, like many good stories do, in a pub. As early as the Middle Ages, Szymanski explains, the rough outlines of soccer—a game, a ball, feet—appear to have been present in England. But it wasn’t until the sport became popular among aristocratic boys at schools like Eton and Rugby in the nineteenth century that these young men tried to standardize play. On a Monday evening in October 1863, the leaders of a dozen clubs met at the Freemasons’ Tavern in London to establish “a definite code of rules for the regulation of the game.” They did just that, forming the Football Association. The most divisive issue was whether to permit “hacking,” or kicking an opponent in the leg (the answer, ultimately, was ‘no’).

But that wasn’t where the controversy ended. In 1871, another set of clubs met in London to codify a version of the game that involved more use of the hands—a variant most closely associated with the Rugby School.

“From this point onwards the two versions of football were distinguished by reference to their longer titles, Rugby Football and Association Football (named after the Football Association),” Szymanski writes. “The rugby football game was shortened to ‘rugger,’” while “the association football game was, plausibly, shortened to ‘soccer.’”

Both sports fragmented yet again as they spread around the world. The colloquialism “soccer” caught on in the United States in the first decade of the twentieth century, in part to distinguish the game from American football, a hybrid of Association Football and Rugby Football. (Countries that tend to use the word “soccer” nowadays—Australia, for example—usually have another sport called “football.”)