When my Hagrid was young, he is a 12 year old Border collie his best friend in the world was Philly a young Pit Bull. Those two would always play hard and now stop.
Hagrid loved Philly he couldn't have a better playmate. After coming in from a long walk the two were still bouncing off the walls crashing around the living room. Unfortunately Hagrids loop on his collar got caught on Philly's tooth, she couldn't get it off and was dragging Hag from room to room.
Having the tight clamp of a Pit's jaws it was hard to pry open her mouth and remove the loop caught on her tooth. Philly's owner was able to do it, but had he not Hagrid would have died.
The moral to this story is Never again did Hagrid wear a collar while playing with other dogs.