Yeah, a long time ago, when I was working security at a very large hospital, we had a person kicked out of the ER for abusing staff. In the drive way to the ER he started refusing to leave. We radio the local police patrol. Three cops show up. After about 45 minutes of trying to talk him into leaving, he pulled out a knife and lunged. So I punched him in the side of his head, towards the back. He dropped dead. He had an aneurysm and that blow ruptured it, instantly killing him.

Luckily for me, the person he was trying to stab was a cop, so there was no question of criminal charges.