"... the field is bare by August ..." isn't a conclusion of any kind. It either is or isn't. It's information (a factual result, not a conjecture) and therefore a premise supporting why the turf should be replaced. While we know the argument is about replacing the turf, how many matches are hosted is context for these premises but is not, in and of itself, a premise. How are we to assume that sixty matches plus concerts are "heavy use?" Maybe 100 or 1000 are. For me, this renders it context for the premises.