Why did the normally mellow Mountain View cat suddenly attack his owner?

DEAR JOAN: It’s 10 p.m. and my always indoor cat, Butter, is growling at the screen door in my bedroom. I turn on the outside light and see two huge raccoons in the yard.

Suddenly the kitty turns on me and claws my leg with both paws, leaving deep puncture wounds, then he jumps up on the bed and falls asleep, as is his normal pattern.

I saw a doctor and got an antibiotic, so I’m OK, but my question is, why would my normal, loving, mellow cat attack me when he was obviously upset...