I haven't read ALL the responses, but:
1) I don't think pit bulls don't belong in dog parks period end of story. I know plenty of pit bulls who do fine in day care or dog parks.
2) Any dog who is reactive to other dogs in the way you describe, ESPECIALLY a terrier breed and ESPECIALLY a dog who is 8 or 9 months old (reaching sexual maturity, fully developing their prey drive) DOES NOT belong at a dog park.
It doesn't matter if 9/10 times he doesn't act like that around other dogs. What happens when he runs at the 10th dog and is so amped up he can't help grab it by the throat or head and kill it? You are perfectly describing how every single pit bull (or dog of any breed) acts when their dog aggression first begins. These are all signs that this dog is developing an inability to control himself around other dogs, and the fact that he bit YOU hard...well, what do you think he was going to do when he got to the other dog? Exactly what he did to you.
Every time I hear some person with a pit bull that kills another animal, or redirects a bite onto a person that is BAD (like, needs medical attention bad) and they say "oh my god, HE NEVER BIT ANYONE BEFORE, HE WAS NEVER AGGRESSIVE, *sob sob sob* we never saw it coming, HE JUST ATTACKED OUT OF NOWHERE." no, he didn't attack out of no where, there was a bunch of warning signs, and those warning signs are all the behaviors you are listing Baloo doing.
I don't think this necessarily means Baloo won't be ok around other dogs, ever, but he is CLEARLY telling you that the dog park is past his threshhold, and continuing to expose him to that environment is seriously increasing your chances of him becoming either very DA or redirecting a bite onto a person. AND, if he hurts another dog or person, and they find out you had seen this warning signs and CONTINUED to take him to the park, you will be liable, not only for the bite but for endangering the welfare of the people/animals at that park by taking him there. You're not only putting everyone else at the park at risk by taking him there, you're both setting Baloo up to fail AND putting him at risk.
Pit bulls don't just snap out of no where. They give warning signs such as playing too aggressively with smaller dogs, getting overexcited when not allowed to approach other dogs, and if he's biting you as a redirect, he's obviously not past coping with his excitement by aggression. At what point will you say "he's obviously not a dog-park dog"? When he tears a small dog apart and ends up getting put down?