Gorillas can run at speed in excess of 20 mph and can reach a top speed of 25 mph when needed. read more
Unless the gorilla is somehow hobbled (drugged, lamed, etc.), or the human fighter is armed (especially with something like a spear that can hold the gorilla off at a distance), the gorilla will kill the human and then be vaguely dejected that the human wasn't able to put up enough of a challenge to be interesting. read more