What is the main conflict in the story "The Most Dangerous Game"?

The question is correct to suggest that there is more than one conflict present in this story. The main conflict is the man versus man conflict that exists between Rainsford and Zaroff. Rainsford falls over the side of the ship that he was on, and he is forced to swim to the nearby island. Rainsford discovers that the island is inhabited by a fellow gentleman that also happens to be an avid hunter. Unfortunately, Zaroff's favorite prey is humans. He forces Rainsford to be his prey. Rainsford must survive for 72 hours. If he is successful in doing that, then Zaroff claims that he will release Rainsford from the island.

"And if I win—" began Rainsford huskily.
"I'll cheerfully acknowledge myself defeated if I do not find you by midnight of the third day," said General Zaroff. "My sloop will place you on the mainland near a town."

The bulk of the story details how Rainsford tries to outwit Zaroff. Zaroff is a good hunter, and Rainsford works very hard to throw him off of his trail. The conflict is a dire conflict because if Rainsford fails . . . he dies.