What is the law of the club and fang? What does it have in common with primitive law from chapter 1?

The Law of the Club and Fang is the life Buck enters when he is removed from the Judge's estate. He can fight and bare teeth (fangs), and because of it he can be beaten.

What it has in common comes at the end of Chapter One, and the man in the red sweater. Buck has never known anything but love and family; his first experience with primitive instinct comes with this man and the way he treats him. Buck is initiated into an animal's baser instincts by the man who tried to break him but couldn't.