Thanks, as always, to everyone for the helpful and supportive replies.
Obviously easier with hindsight, but I think it's pretty clear that I should have found a way to deal with the half time behaviour. Even now I'm not sure how I'd have gone about that being on my own with no assistants, but one to consider for the future. I've flagged this behaviour (as well as a few other bits) to the league's safeguarding officer.
Also noted on the half time drinks point. I'm usually pretty limited in terms of where I can go as I try not to set myself up on the parents' side of the pitch, but grabbing my drink and heading back into the middle is a good idea.