My cat viciously attacked my husband.

My husband stubbed his toe tonight, reached down and winced, and my cat took the opportunity to viciously attack him. I have never seen such a bad attack from a cat in my life. His arm is seriously cut up to the point where he might have to get stitches. It was seemingly out of nowhere, and he is usually not an aggressive cat. He did this once to me before, when we were outside and I fell and he came over and attacked me. Does anyone know why he would do this? It is honestly terrifying because if he had gotten to his face it would’ve been devastating. We don’t know what to do but we cannot have a cat attacking like this.