No idea if the following is true, mind
The word “soccer,” which is believed to have originated in Britain some 200 years ago, comes from the official name of the sport, “association football.” As other versions of the game evolved to include Rugby Football, it is believed the Brits adopted colloquialisms to distinguish each game.
“The rugby football game was shortened to ‘rugger,’ a term recognized in British English to the present day, and the association football game was, plausibly, shortened to ‘soccer’” Szymanski writes. (Apparently ending words in “er” was a fad back then.)
Gradually, the term “soccer” gained popularity in the U.S. to distinguish the sport from American football. By the 1980s, the Brits began to part with the term, apparently, because it had become too “American.”