Grendelkin strength

And with that, the grendelkin rushed me. A crushing fist the size of a volleyball flicked at my face. I was fast enough, barely, to slip the blow. I flung myself to the cavern floor, gasping as the shock of landing reached my shoulder. That sledgehammer of flesh and bone slammed into the wall with a brittle crunching sound. Chips of flying stone stung my cheek.
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.

Side Jobs, Heorot, Page 141