Harry made up his mind in a split second. Before Snape could take even one step towards him, he had raised his wand.
"Expelliarmus!" he yelled--except that his wasn't the only voice that shouted. There was a blast that made the door rattle on its hinges; Snape was lifted off his feet and slammed into the wall, then slid down it to the floor, a trickle of blood oozing from under his hair. He had been knocked out.
~Prisoner of Azkaban, Ch. 19 "The Servant of Lord Voldemort"
You just have to feel really sorry for Snape here... I know he was being unreasonable, but he had just found the man that had supposedly been the reason for Lily's death. Anyone in his place would have gone just as mad.
I posted the part before this quote at least 21 weeks ago, so I guess this is a continuation. This deserves its own post, because this always makes me really mad at Harry and really sorry for Snape whenever I read it.
