The story seems to be constantly evolving, as one side accuses the other of gross misconduct, and the other accuses it's opposite of being uncaring, unfeeling little dictators with guns, so I figure the truth must lie somewhere in the middle.
So far as I can tell, the general outline of this sordid tale goes something like this:
Some complete ignoramus decided to take her three pit bulls out for a walk in a public park. At least one of the animals was unleashed. As is common when multiple dogs are in such close proximity, a fight broke out among at least two of the animals, and at least one of them turned on it's owner who tried to break the fight up.