I saw this a few games last year with Seaside now Valencia and Gold Coast bring their clubs flags to away games. To me when you visit another teams field you are a guest and you should respect their place. I think these flags are going to cause problems, I had one of our parents say they wanted to throw the flag down and stomp on it. I can only imagine the middle aged out of shape fight that may take place over these things. Cringing that it would happen and a video show up on the nightly news
I have no issue with it at Tournaments which usually is just to mark a meeting area.