He'd learned that the object of a school fight was not to gain points for style but to force your enemy to give in, which meant hurting him more than he was hurting you. He knew that you had to be willing to hurt someone else, too, and he'd found out that not many people were, when it came to it; but he knew that he was.
So this wasn't unfamiliar to him, but he hadn't fought against a nearly grown man armed with a knife before, and at all costs he must keep the man from picking it up now that he'd dropped it.