At what point is contact considered abuse and when should police be called?

This has recently come up with some people who are very close to me and I am interested in opinions.

Is this a zero tolerance issue or is there certain level of escalation that warrants police intervention? Does there need to be danger or just physical contact? Is any angry physical contact considered abuse or is the word abuse reserved for more serious offenses?

A wife slaps a husband once? Husband slaps a wife? Teen slaps sibling? Parent to child, child to parent? What if it any of those situations were a punch? Or a push? How about repetitive beating? Throwing objects? Where is the line?

If the answer is zero tolerance, is one push or slap in an otherwise reasonably happy and nonviolent home worth the risk of well-adjusted and well-cared for children being placed with social services for the night? Which is worse? Do you (wo)man up and say, “so I got pushed – whatever” and chalk it up to one bad night out of many good ones or is zero tolerance zero tolerance and that’s that?

If you are one who still considers it zero tolerance, how do you feel about verbal or emotional abuse? Is one “Fuck you” verbal abuse? Is one “you’re a waste of air” mental abuse?