Americans are regularly told that soccer is an American corruption of a proper name. The word is English in origin, and its survival on one side of the Atlantic has a straightforward explanation.
The word was coined where the sport was codified
When the game was written down, it was distinguished from other football codes by the word association, describing the body that had agreed the rules.
Students at English schools and universities of the period habitually abbreviated words and added a suffix, producing clipped forms that sounded casual and slightly private.
Association shortened along exactly that pattern, and the result was used comfortably in England for a long stretch by players, writers and administrators alike.
Several codes needed telling apart
The reason a distinguishing word was needed at all is that football was a family of games, and different schools and towns played versions with different tolerances for handling and tackling.
Rugby football and association football separated formally, and other codes developed independently in Australia, Ireland and North America from the same shared ancestry.
In any place with more than one code in circulation, plain football is ambiguous, so a specific word becomes genuinely useful rather than merely pedantic.
America had its own football to name
The American game descended from the same rugby-influenced family and took the plain name football early, leaving the association code needing a label of its own.
The imported English abbreviation was already available and fitted the gap, so it stuck without anyone deciding anything.
The same thing happened in other countries with a dominant rival code, which is why the word is normal in several places and not only in the United States.
England dropped it as the ambiguity faded
As association football became overwhelmingly dominant in Britain, the plain word stopped being ambiguous and the abbreviation became unnecessary.
It then acquired an association with America, and usage declined further for reasons of identity rather than of language.
The complaint about the word is therefore a fairly recent development, and older English writing uses it without any self-consciousness at all.
Naming disputes follow the sport everywhere
What a sport is called usually reveals which code arrived first in a place and which institution had the authority to name it.
Similar arguments run through other sports where a governing body's formal name competes with what players actually say on a field.
The vocabulary is a record of competition between codes, and the winner in each territory is written into ordinary speech long after the contest is forgotten.

