Dog was on a lead, probably 1.5 metres ahead. Family of 2 adults and 2 children walking past in opposite direction. Children probably 4 and 8? As they walked past the younger girl darted towards the dog and put her hand on his head (flat palm almost like she was hitting him but I think she was trying to pat him on the head) and he nipped her. We were passing each other on a path in a park so were quite close already. Had zero time to do anything as from her walking past to touching him happened in about 1.5 seconds. We had no interaction with the other family prior to this. Dog has never bitten before, we think he just got a fright from the girl, but the family went mad and started threatening to call the police saying we have a dangerous dog (he's am old staffy who has never bitten once and we were so shocked that he even nipped her as he is extremely gentle!). Family followed us round the park and kept shouting 'we know where you live, police are going to be well aware of you'. The girl wasn't injured, skin wasn't broken, but she was obviously scared. Surely this is the fault of the family for not teaching their children not to touch dogs? I don't have a dog so haven't really had to think about it before, but my son knows not to touch dogs without confirming with the owner that they're friendly. It is drilled into him!