In person-to-person conversation, there's little room for ambiguity where "football" is concerned. If you're conversing with a friend, the two of you know exactly what game you're talking about. Confusion only arises when the word is used by the media and, even then, it's fairly easy to decode. If the announcer sounds like he's from Nebraska, he's talking American football. If he sounds like he's from Leeds, he's talking "soccer".