What did billy do to save the dog in the middle of the fight and what did he do to take care of it?

Billy scares off the other dogs and calms down the dog. It is starving, has apparently traveled a great distance, and wears a leather collar with the name "Buddie" childishly scratched in it. Billy takes him home, feeds him and bathes him. The next night, Billy tearfully lets him go on his way.