When you get sprayed by a boomer crouch!
This was going to be a long tip, but bundy seems to have covered most of it.
Yes meleeing does kill zombies!!
But you are meleeing to keep them off of you while the others, if there are any, kill the zombies..... so stay in a corner ( so zombies only have one path to you ). Stay crouched ( so we can get head shots on zombies. ).
Happy Fragging
MAN