Several explanations have been given for this behavior. Some believed raccoons had insufficient salivary glands, but this was disproved. Currently, this behavior is believed to be a replacement for the natural behavior of catching crayfish or other aquatic prey. People have often made young raccoons, curious and intelligent, into pets. Adult raccoons can be savage fighters if cornered.
Few dogs can successfully attack an adult who is ripping and slashing with their teeth and claws.
Raccoons may even drown their opponent if in water. Raccoons may live up to 16 years in the wild, but most don't make it past their second year. Wild Mammals of North America. Johns Hopkins University Press, Baltimore. The New Encyclopedia Britannica.