There is not much history of US athletes or spectators singing the national anthem because the tradition here is to have a performer singing it. Almost everywhere else the tradition is for a band (or recording) to play the music and the crowd and players to sing.
Having been in an Irish stadium with the crowd singing and watching a French crowd belting out La Marseillaise I prefer the foreign way of doing it rather than have some performer putting on their over the top spin on the Star Spangled Banner.