Well I was in an off-lead area once and a family shows up. They had no dog, they were just looking for a park to play soccer. Unfortunately as soon as they started, half the dogs in the park went after the ball. Sammy got there first, picked the ball up immediately and started trotting around proudly. I told him to drop it, but I knew the only reason he could hold it up was because his teeth had already gone through. The family got so angry at us, not just me, but all the dog owners. He said the dogs should be on a lead, and when it was pointed out to him that this was one of the few places in the whole city where our dogs didn't have to be on lead, he went on to say he thought that was a dangerous and stupid idea (English was not his first language so it was hard to understand what he was yelling about). I then admitted to owning Sammy and offered to buy him a new ball but his response was that he would never be coming back and there was no way he was going to tell me where he lived, obviously he didn't believe I would be coming around to drop off a ball.
I think your dog/s should always be under effective control but given there are so few off-lead areas, I also think that if you don't have a dog and you want to do other sorts of activities in a park, well unlike the dog owners, you do have a lot of options. Sammy doesn't run into people much anymore which is lucky, but he did as a younger dog. He seemed to have a lack of spatial awareness and he grew so fast and so big it was like he just had an ever increasing mass to be aware of. Add that to the fact that if he tried to turn whilst running he fell over and the fact that he always stayed near me, well you see how I ended up with bruised shins. I mean if I had ever seen someone who was obviously disabled at a park when Sammy was younger, I would have left and gone elsewhere because there is a real risk and you can't train puppies/adolescents to be more spatially aware or tell them off for wanting to run around in the one place they really can.