From Judge Roger Benitez's decision in Fouts v. Bonta(S.D. Cal.):
This case is about a California law that makes it a crime to simply possess or carry a billy. This case is not about whether California can prohibit or restrict the use or possession of a billy for unlawful purposes…. Historically, the short wooden stick that police officers once carried on their beat was known as a billy or billy club. The term remains vague today and may encompass a metal baton, a little league bat, a wooden table leg, or a broken golf club shaft, all of which are weapons that could be used for self-defense but are less lethal than a firearm….
The court struck down the law on Second Amendment grounds (citing, among other cases, Caetano v. Massachusetts (2016), which suggested that stun guns were constitutionally protected arms). The historical analysis is long and detailed (read it here), but here's the conclusion:
