From the decision of judge Roger Benitez in Fouts v. Goodness(SD Cal.):
This case involves a California law that makes it a crime to simply possess or transport a billy. This is not a question of whether California may prohibit or restrict the use or possession of a billy for illegal purposes… Historically, the short wooden stick that police officers once carried with them on their ride was known as billy or billy club. The term today remains vague and can include a metal stick, a small alloy bat, a wooden table leg, or a broken golf club shaft, all weapons that could be used for self-defense but are less lethal from a firearm… .
The court struck down the law on the basis of the Second Amendment (citing, among other cases, Caetano v. Massachusetts (2016), which suggested that stun guns were constitutionally protected weapons). The historical analysis is long and detailed (read it here), but here is the conclusion:
The Second Amendment protects the right of citizens to defend themselves with dangerous and lethal firearms. But not everyone wants to carry a firearm for self-defense. Some prefer less lethal weapons. A billy is a less lethal weapon that can be used for self-defense. It is a simple weapon that almost anyone between the ages of eight and eighty can make from a wooden stick, clothes pole, or stick. One can easily imagine countless citizens carrying these weapons on daily walks and hikes to defend themselves from attacks by humans or animals. To give full life to the fundamental right of self-defense, every single responsible and law-abiding citizen has the constitutionally protected right to keep and bear weapons such as the billy for lawful purposes.
In early America and today, the Second Amendment right to self-preservation allows a citizen to “‘repel force with force’ when ‘the intervention of society on his behalf may be too late to prevent such harm.’ “The country anticipated that, as our nation matured, circumstances might make prior recognition of rights undesirable or inadequate. For that event, the Founders provided a built-in means by which the Constitution could be amended, but a single state, no matter how well-intentioned, might not do so, and neither could this Court.
Alan Beck and Stephen Stamboulieh represent the plaintiff.