I live in NYC. I just got a dog from a rescue. Sweet, mild, unfixed pit bull mix. She's not in heat, I know because her two month old pup is with us and counting back, she shouldn't go into heat for another 2-3 months. At the dog run today for the first time, though, all the dogs ganged up on her, becoming more and more aggressive until they were nipping at her trying to bring her down! One dog definitely instigated it, but by the time I told the owner, it was too late. A civilized city park turned into a wild pack of dogs aligned against this sweet mild dog who I've never heard even bark. Did I do something wrong? Should I have stepped in at the first sign even though the other owners were there? Should I have taken her out at the first sign, or should I have introduced her around slowly. What do you do to avoid a pack mentality forming?

That sounds very scary. I'm sorry I don't have an answer, but is your pup OK?

She's not fixed, so even though she's not in heat, she still gives off a scent that can drive other dogs a bit mad.

I would get her fixed as soon as possible.

Also, it's always best to introduce dogs slowly. I love the off leash park, but if your dog is new it's best to meet one or two dogs at first, then work your way into the group.

Not all dogs are accepting of a new dog, especially an unspayed female that recently had a pup.

Correct the instigator after the first sign of aggression. It will take a while for them to get used to her. But in the meanwhile, let all the other dogs know that YOU are Alpha.

And I agree with getting her spayed, ASAP.

Sadly the same thing happened to me a week ago.
We take the dogs to a park near here that's all fenced off and designated for dogs. Usually there are several other dogs there and our dogs love playing with the others, it's a real doggy party.
Last time we were there there were these 2 horrible dogs there (owned by the one person) and they just tried to dominate the other dogs. It pushed my dogs to the ground and held them there.
The owner did nothing to stop their dogs!

No you did nothing wrong... some people are just idiots and take their dogs to the park even though they are not good around other animals and are not trained properly.

I would however get her spayed as soon as possible as others suggested just in case it was to do with the fact she was giving off a different scent.

Thank you for all your kind suggestions. She's definitely going to be spayed soon, it just came as such a shock, barely two weeks after coming to my home. Next time I won't hesitate either when another dog misbehaves - whether the owner is there (in this case she was just beside me!)

Humans will never be able to break up the natural want of becoming a pack. If you allow a dog to become wild, they will survive. Don't blame yourself for this incident... things happen, and dogs will always be dogs. Sometimes when a group of dogs have created a pack, they will pick on the more timid, shy and weaker dogs. To them, that dog is going to cause them a lot of problems. You may also want to get your dog checked out by a vet. Sometimes dogs will pick on the sick dogs too. A blood panel would be able to see what's going on inside.

I avoid dog parks all together... for one, my dog would become the instigator.. two.. there are just too many ill mannered dogs and owners out there that don't understand much of dog language. Dog parks are just a given that there is going to be some type of fight... its just a territory thing.

You've gotten good adivice and I'm no pet expert. But I am an expert on using forums like this. So I have a question. This is a site for asking questions. This forum is for asking questions about dogs. So what good does a subject like "ask about dogs" do for your question? By posting a question here we already know you want to ask about dogs.

Don't you think a subject like new dog attacked by pack would have better let us know what your question was about? Did you bother noticing how other people used the subject line?

I post this, first to help you use this site more effectively in the future and, second, to help others learn how to use it more effectively.