Since I was in law enforcement from early 1971 to late 2001, I saw the evolution of laws pertaining to "Domestic Violence".
You see, up until the 90's, it was semi-accepted--unless a husband or "Live-in" did a serious bodily injury to their other.
Women would complain, neighbors would call, police would respond, often resulting in an arrest of the inflicter of the injuries. Later, again very often, the injured would refuse to sign a complaint, resulting in the release of the inflicter and no charges being filed
Usually, this was because the injured realized that the inflicter was her "Meal Ticket", or --here was a classic case: I--along with several others--were dispatched to a shooting. Husband, who is hard-core unemployed, and baby sits their children, has struck up a frequent meeting with a neighbor lady. Wife comes home early and surprises them. She rages at hubby, and keeps it up--neighbor had fled.
Hubby tells wife to shut up, like they say, Hell hath no fury. Hubby goes to a drawer, brings out a .25 auto pistol and shoots wife--twice.
L A County Sheriffs enter the apartment, then call in L A's first Paramedics. Wife is removed on a gurney . She is now down to street level. Hubby is brought down with a gun to his back and in handcuffs. Wife on gurney--yells repeatedly--"Don't hurt him--I love him".
The 90's arrive and this becomes an issue in California. Like most things the California legislature deals with, they do overkill.
NOW, the parties do not have to be married. All that is required is if they live together. They do not have to be of the opposite sex.
IF a Peace Officer is called to a dispute, and one party has a "Visible Injury", that Peace Officer MUST:
Arrest the other party
Offer to take the injured party to a shelter
Offer to call a judge and obtain a Restraining Order
The injured party is now not the Victim. The State is, and the prosecutor of the jurisdiction will file charges
(NOTE: IF the accused inflicter is a Police Officer, and a Restraining Order is issued--he/she can not carry or be in possession of a firearm. Consequently, his/her Department will terminate them)