[PennysMum]

It may not have necessarily been that the other dog was poorly socialized-- the leashing/non-leashing thing may actually be at fault! Dogs are just more likely to get into confrontations when one dog is on lead and the other dog is not. The leash makes it hard for the dogs to communicate as they normally would-- the off-leash dog will try to circle the other dog for sniffs, the leash gets in the way, pups end up twisted up and nerves run high because one or both dogs can't move as they normally would. If both dogs are on leash it is less stressful. Likewise if both are off leash it is less stressful. In this case, the stress was probably compounded by the fact that there were even more dogs there, and the nippy little guy felt extra confident with his pack to back him up!

He might have been a perfectly nice little dog if he had been on a leash when he met your leashed dog, or if all the dogs had been somewhere safe for off-leash play. I'm certainly not saying that the owner isn't at fault for letting her dogs play off-leash where it isn't appropriate, but the stressful on-leash/off-leash dynamic is something worth being aware of, and can help you defuse (or completely avoid!) potential confrontations.