I am looking for help because my (usually well behaved with all people and kids) dog did something out of character today. Snow is new to him, but we were outside playing in the snow and there was a family right next to us and the kids were sledding down the hill. Well Inuki (my german shepherd/whippet mix) charged at the sledders and barked then ran away. I could see he was extremely nervous about the family, even though they paid no mind and were very friendly to him, his hair on his back stood up when the woman came to pet him, and his tail between his legs, then he charged another sledder barking and pretending he was going to bite/nip. I dont know what his intentions were, but he seemed fearful/nervous/aggressive, and I have never seen this side of him surface. He has always loved kids, strangers, and everyone, at least since I had adopted him. I am in fear that this behavior could worsen unless I can find some help. He only has acted strange around this family, but they always ignore him and so they do nothing to provoke him, and the kids are very good with Inuki. I am so confused as to why he would act this way.