My husband is harsh towards our son and threatened me

Tonight, my husband seemed to put our son down through an incorrect approach. His approach was perfectly wrong. I found myself defending my son. I told him that what he did was not the way to encourage our son. Instead of watching my husband's harsh behavior I decided to sit beside my son and, together, we worked on his science assignment in order to encourage him to study. My husband got upset and he was swearing at me. He threatened me. I knew that he was not joking. His words scared me a lot!