I, too, had a bad experience at the dog park in our city.
Buster's 1st time there. He and the other dogs smelling each other. The group of 4-5 dogs and their owners were congregating right by the entrance, which is one of the things posted as a no-no. We were there about 5 seconds and one guy says we have to leave because we have an aggressive dog. Buster hadn't done anything even close to being aggressive. I told the guy "look, they are all smelling each other - no one is being aggressive". I tried to get Buster to come with us and explore other areas of the park, but he and the others were still checking each other out. The guy continues on about us having to leave because Buster is aggressive, how we're supposed to have control of him. We got into a shouting match, unfortunately. Then one of the smaller dogs ran at Buster and the typical "noisy" boxing match started. The smaller dog rolled over in a submissive position with Buster just standing over him. No more growling, barking or anything by either. The guy had his back to the whole thing and I started to head over to get Buster (about 5 feet away). The guy turns around and kicks Buster in the head and yells because the other dog is his. I had all I could do to keep myself from pummeling the guy (I'm a female that stands 5'2" and he was 6' maybe). My stepdaughter got nose to nose with him and she was yelling at him for kicking HER dog; she was practically crying, asking the guy if he goes around kicking dogs, etc. The other people there sided in with the guy, saying they would defend their dogs, too, and I really felt like I was being ganged up on big time. I had all I could do to get Buster and leave the park. There was no bloodshed, no biting, nothing. Just the typical boxer noisy scuffle for about 3 seconds. But this guy had already determined when we arrived that our "big boxer" was aggressive. He said he wanted my address so he could report me. I wanted to say, "yeah, well I want a world where people all have brains and use them, so I guess we can't have everything", but I didn't. Why try to reason with a moron.
I won't go back there again; it's not worth it!