Fights often happen within families, and when they rise to the level of physical aggression, the police are often called, and someone ends up in jail.
In California, the term “domestic violence” can involve a variety of offenses, including simple assault (California Penal Code Section 240), simple battery (California Penal Code Section 242), assault with a deadly weapon or by means likely to cause great bodily injury (California Penal Code Section 245) battery on a domestic partner (California Penal Code Section 243(e)(1), or spousal battery (California Penal Code Section 273.5.
While all of the above code sections require some form of assaultive conduct, they differentiate crimes by the severity of the conduct and the status of the relationship with the victim.
Penal Code Section 273.5 generally only applies to people who are legally married to each other, while Section 243(e)(1) applies to battery against a live in partner, or people in a dating relationship, or people who have a child together.
Section 240 and 242 would apply to people who are unrelated, or to people who are related but not in the above categories, such as a brother, sister, cousin, parent, child, aunt or uncle.
Defenses to a domestic violence case are almost always factual in nature. When the police arrive at a domestic violence call, they usually separate and talk to the parties involved, then decide who to arrest based on what they are told. They do not always make the right call, and this is what jury trials are for.
If you have been arrested for domestic violence, you need an experienced attorney.