Here you CAN reserve the covered picnic tables for parties, but they put up a sign that says "reserved" on the ones that are, and only the covered ones can be, there are still lots of benches and tables.
So, like, if you were sitting at one someone did pay for they could ask you to move, but it wouldn't involve the police.
I love the park here that is run by the city, not the county. There are always men playing soccer, people having parties with music, and on Wed evening there is a group of high rolling Pokemon go players there for Raid day, go play with them and you cannot lose, it's great. And when it floods in the summer it is gorgeous.
Parks are "third spaces" for sure.
Aargh what fuckers. If the park is public, it is for us to use. Wasting police time too.
If you are feeling up to it, complain to the city government. Tax money pays for these spaces and you pay taxes.