Verbal Abuse vs. Physical Abuse: Where Is The Line?

But I tell you that anyone who is angry with a brother or sister 

will be subject to judgment. Matt. 5:22

Our sermon a few weeks ago was about anger, and the verse from Jesus' Sermon on the Mount.  Patricia Evans in "The Verbally Abusive Relationship" (2006) explains how subtly, slowly, verbal abuse starts, and how, in some cases, it slyly escalates into physical abuse. It starts with being in the "zone" of the other person, purportedly unaware of the other body in the space. Then it might manifest as blocking a doorway or a path, and might move to "accidentally" standing on the spouse's foot.  Before I read this book, I imagined that a physical abuser started out punching his wife on their honeymoon.

For Mother's Day I received a small welt on my face.  Technically, it was an accident, but anger and frustration were involved.  I will describe the event; do you think it is abuse?  I am so new to even thinking in this way.

I was kneeling on the ground weeding. My husband was standing and weed-whacking with a machine 10-12 feet away.  I called out to ask him to stop whacking.  As he stopped, he anticipated my reason, and he threw the machine in my direction with a great deal of anger. It landed on the ground several feet in front of me.  I was startled, but didn't react.  A few minutes later, when our discussion about weed-whacking was done, my husband headed to another spot about 3 feet away from where my face was bent over a flower bed weeding and he started up the machine. Instantly the spinning line of string kicked up small rocks and bark into my face.  One small stone hit my face hard. I fled into the house upset. My husband came in soon after and apologized; he claimed the first toss of the machine was not throwing "at" me, as he was well aware the machine could not travel that full distance, and the second event was entirely an accident.  His apology seemed genuine.

What do you think?  We all do things in anger that are not abuse.  We all make mistakes that might cause minor hurt to one another.  Where is the line? What is a choice and what is an accident?  The variations are infinite - how would you make this distinction?