How is Rainsford and Zaroff (man vs. man) the main conflict of the story in "The Most Dangerous Game"?
I think the real conflict of the story is Rainsford's conceptualization of how hunting affects the prey.
The author's purpose of this story is to position man as prey and make the audience question if hunting is ethically right or wrong. Of course man does not hunt man, but to put the image out there makes the audience consider that our efforts to hunt animals may just in fact be a step toward going somewhere further if necessary.
Thus, Rainsford is positioned to consider something he never even gave merit to, what prey feels like. In the very beginning, Rainsford's friend Whitney presented the idea that animals can feel. At least if nothing else, he thought a jaguar could feel fear.
Rainsford may not necessarily be in conflict with man as in another man, in this case General Zaroff. But he may be in conflict with man, as in mankind. To hunt, I believe the author is suggesting, is to make sport of taking another life, regardless of species. So Rainsford's conflict is with himself and his ethical perception of hunting, and it is also with an innocent generation, of which he has now been made part.