POTENTIALLY DANGEROUS AND VICIOUS DOG

How is that a POTENTIALLY DANGEROUS AND VICIOUS DOG is allow to be off leash in section B at Memorial Park just a few feet away from so many kids? I have a huge concern that LuLu a large and very strong and at time aggressive pit bull  should not be allow to be off leash in any public area.
Today is the second time that I'm aware of that this dog has gone viciously after another dog.  The owner says it's because Lulu is ball aggressive, then my question is why bring a ball and toss it for her. He is fully aware of his dog and how she behaves and yet continues to brings Lulu.  Today was a very close call. It's owners such as Lulu's that make it hard for responsible dog owners to have a open and safe place for dogs to  socialize and play. Be on the look out and watch your kids from  Lulu as he enters and exit from the park side.