Fleas??Do you have him on flea prevention??
Dogs get itches just like me and you, and have to chew or scratch to releive them.
If you dont see bad skin or fleas, try an oatmeal bath to soothe. What food is he on??? Sometimes that can make them itchy.Allergies to food.
How old is he??I have a 18week old pup who stuffs his whole paw in his mouth, so playing and such isnt out of the ordinary.
Keep an eye on him, if you notice anything, call and visit your vet.
It could be a many of things. Too many to list w/out any symptoms, it is hard.