The Time Traders by Andre Norton

Ross dropped from the web-slung chair to the floor and made himself as small as possible under the platform at the front of the cabin. Here, where there was a smaller control board and two seats placed closely together, the odd, unpleasant odor clung and became stronger to Ross's senses as he waited tensely for the climbers to appear. Though he had searched, there was nothing in sight even faintly resembling a weapon. In a last desperate bid for freedom he crept back to the stairwell.

He had been taught a blow during his training period, one which required a precise delivery and, he had been warned, was often fatal. He would use it now. The climber was very close. A cropped head arose through the floor opening, and Ross struck, knowing as his hand chopped against the folds of a fur hood that he had failed.