There was a vid posted on here about 2 years ago I think... black cop in a residence of a white woman... I believe she had a knife, and she was coming at him, and he shot her.... bitch did a front flip and landed in front of him. I honestly laughed my ass off.
I'm not laughing for this one, but it's the same sort of situation, except instead of the person coming at the cop, she was going towards another girl with her knife raised. Immediate threat to the girl's life.
edit: here you go (gotta clip the watch on youtube link and confirm you're grown)