Domestic violence is one of the most misunderstood, misapplied (by the prosecutor), and highly emotional crimes of all. The very topic evokes irrational emotion and logic (at times from judges!). While true, this friction is because not only do we all know someone who has been the victim of Domestic Violence, but we also know someone who has been the victim of spiteful and false accusations of Domestic Violence.
There are two common charges to domestic violence. The first is usually called a 'domestic battery' under Penal Code Section 243(e)(1), someone can be arrested or charged for this offense if they, 1) willfully inflict, 2) force or violence, 3) on a person they have had/have a relationship with. The other type of domestic violence charge is the 'Corporal Injury to a Spouse, Cohabitant, or fellow Parent.' This is found under Penal Code Section 273.5.
To be arrested or charged with this offense, they must, 1) inflict bodily injury on a current/former spouse (or) current/former cohabitant (or) the mother/father of that child, 2), they have willfully inflicted the injury, and 3) the injury resulted in a traumatic condition. The traumatic condition is a wound that resulted from an application of force. To make it easy, the condition must usually be visible.
As one can imagine, when two lovers, parents, or intimate partners quarrel, all boundaries are forgotten. Therefore, physical violence sometimes makes emotional and logical sense to one or both people. Unfortunately, sometimes picking up the phone and accusing the other person of committing a crime against them is also, in that person's mind, fair.