There's a semi-famous story about an Aikidoist who was stabbed and killed. This was in New York and I believe it was in the 60's. The guy found a kid around or in his car. The guy, a 3rd dan, confronted the kid and the kid did what you do with knives.
I know of another Aikidoist here in the Bay Area who was attacked in bed by her boyfriend and killed. She was very much a beginner from what I know.
No fights nor even serious possibilities since I've been doing this stuff.