Wolfgang....football & rugby songs really do fall into what I call the 'tending toward' folk songs category just because of the criteria you mention-and a couple of other criteria: ease of singibility and non-commercial nature. They fail only on the 'age' criterion...and that will change. They are definitely a distinct sub-set, but I would call (most of)them folk songs.
All this needs more clarification, and I hope one day soon to have my list of 'tending toward' criteria more carefully thought out and complete-(and ready for the tender critiques of this gentle forum ;-).