For all of you who say, it's a public ballfield, let me share a story. This past Spring, we went to my DD7's baseball game at a local school. My DH and I were there with my DS 4 and DS3 as well as other parents, family members, etc in the designated grassy sitting area (small town, no bleachers). One of the women had brought her dog on a leash and was also watching the game. FINE - No problem - I have a dog, love dogs, etc and my kids never approach strange dogs.
Then my DS 4 runs to get something and comes within 10 feet of this dog who leaps and bites him on the leg.

As I'm trying to comfort my son and find out how bad the bite is, the idiot sister of my DD's coach's wife tries to tell me how the dog was "only playing" and "he's a herding dog so he does this". NO - IT"S NOT PLAYING - HE BIT MY SON

She then offer to buy him candy or a soda to make him feel better. Fortunately, the dog has his shots and my DS is basically OK but the coach's wife tells me this dog has done this before.
Let me tell you that dog should never be brought to a place where kids are present. I don't care if she wants to socialize him - he's a danger, he's done it before, if you can't leave him home, don't come to the game. And while it's a public place, a dog is not a person. It is reasonable to assume that there will be young children at a 1st grade baseball game and if you can't control your dog, keep it away from my kids.
Thankfully it wasn't serious and my DS loves our dog so he isn't afraid of dogs for life (which knowing him he would be otherwise) BUT it could have turned out much worse. And before I get flamed for hating dogs, let me tell you I

my lab. She's a part of our family, we leave her with Nana if we go away for even a long day because I hate for her to be alone, my children adore her and my DS2's first word after mama 7 dada was "hoop" for Hooch - the dog.

BUT - the safety and well being of people comes before a pet's rights to be anywhere.