When the NW Skyraiders flew at Riverview Park in Kent, the Park Department required us to be AMA members (and club paid AMA site insurance), but also required that our two grass circles be open to all. We had no control over those "others" AMA membership, but apparently we were to ask if they would show their AMA card, and if they wouldn't, we were to call the Kent Police and have them evicted. Not a good thing, and not something anybody did.
Later, when we flew at Auburn Municipal Airport, we didn't have THIS problem, but club paid AMA site insurance and AMA membership was definitely required. For contests, competitors were considered "guests".
"Two up" flying was specifically dis-allowed at both sites. Riverview Park is right next to the Valley Freeway (WA-167), so combat or racing would not be prudent by anybody's definition. Highway noise was a good thing, otherwise. WE required mufflers for engines over .15 size at both sites. Maybe it's .15 and over. We still couldn't control muffler requirement for non-members. I doubt if the Kent Police would have responded anyway.