So you are reinforcing the stereotype that Americans are completely oblivious to what's happening outside of the states?
Football isn't that popular in America, but not to the extreme like you say. David Beckham was a worldwide phenomenon and one of the worlds biggest celebs even before he left Man United to go play for LA Galaxy. If you ask people on the street in NY or LA, pretty much everyone of them is gonna know who David Beckham is, and that he is a footballer. Americans are aware of the sport, they just don't follow it or have that much of a connection to it. A lot of that is because USA hasn't got much to show for in the World Cup. The Americans like to cheer for their own, and there is certianly nothing wrong with that. If USA somehow or another go on a miracle run and reach the World Cup Final in two years time in Brazil, I'm betting the American people will turn in to watch.
Beckham played for Real Madrid before LA (arguabley bigger though)