hits Grendelkin

It scared the crap out of me, which was just as well. Terror makes a great fuel for some kinds of magic, and the get-the-hell-away-from-me blast of raw force I unleashed on the grendelkin would have flung a parked car to the other side of the street and into the building beyond.
The grendelkin hadn't been kidding about knowing counter-magic, though. All that naked force hit him and just sort of slid off of him, like water pouring around a stone. It only drove him back about two steps—which was room enough to let me drop to one knee and swing my staff again. It wasn't a bone-crushing blow, powered as it was by only one hand and from a fairly unbalanced position.
But I got him in the fire extinguisher.
The grendelkin let out a howl about two octaves higher than his original bellows had been, and I scooted around him, running for the altar stone where Elizabeth Braddock lay helpless—away from Gard. I wanted the grendelkin to focus all his attention on me.
He did.
"Behind you!" Elizabeth screamed, her eyes wide with terror.

Side Jobs, Heorot, Page 141-142