In Richard Connell's short story "The Most Dangerous Game," evidence showing Rainsford either killed General Zaroff in cold blooded murder or in self-defense definitely points both ways.
One critical point of evidence showing Rainsford only killed Zaroff out of self-defense concerns the fact that Zaroff never proves himself to be a man of his word. In fact, he shows himself to be the exact opposite. One reason we know he is not a man of his word, meaning he does not keep his promises, concerns the fact he explains to Rainsford he always tells his victims he will pursue them for three days "armed only with a pistol of the smallest caliber and range." Yet, he further tells Rainsford that in the rare moments when his query starts to elude him, he sends out the dogs to hunt the victim, which is most definitely breaking his promise; it is a method of cheating. Hence, due to these explanations both Rainsford and the reader know that Zaroff is so intent on winning that he will stop at nothing. So, if Zaroff tells Rainsford he wins the game if he can elude Zaroff for three days and that Rainsford will be safely sailed home, we know Rainsford really cannot trust this promise. Therefore, what may look like senseless killing at the end of story is truly self-defense since Rainsford knows perfectly well Zaroff is nothing more than a ruthless lying killer.
On the other hand, we can interpret Rainsford killing of Zaroff from Zaroff's own perspective. Zaroff argues at the beginning of the story that all killing of mankind is murder, even acts of war, as we see when Zaroff asks Rainsford the following:
I refuse to believe that so modern and civilized a young man as you seem to be harbors romantic ideas about the value of human life. Surely your experiences in the war--
Though, we might also agree with Rainsford when he replies that his acts of conquering the enemy in war do not make him "condone a cold-blooded murder" and certainly do not make him a cold-blooded murderer.
Hence, the question as to whether or not Rainsford killed Zaroff for the sake of murder or for the sake of self-defense is not an easy question to answer. If we side with Zaroff, then we can see all killing as acts of murder even when the murdered would have done far more murdering had his/her life been spared. But on the other hand, if we view things from Rainsford's perspective, then we see Zaroff as purely evil; we further see that the only way Rainsford could have protected his own life, as well as many lives in the future, was by killing Zaroff out of what we can call self-defense.
I don't see how anyone can call Rainsford's killing of Zaroff "cold-blooded murder" when it is quite apparent at the end of the story that they are going to fight a duel with swords and that Rainsford wins.
Rainsford did not smile. "I am still a beast at bay," he said, in a low, hoarse voice. "Get ready, General Zaroff."
The general made one of his deepest bows. "I see," he said. "Splendid! One of us is to furnish a repast for the hounds. The other will sleep in this very excellent bed. On guard, Rainsford." . . .
The author apparently wanted to wrap up the story and not get into a long description of a sword fight in the General's bedroom. This might sound like too much of a cliche. Besides that, the story is about one man hunting another as if the hunted man were an animal. Once Rainsford succeeds in escaping the hunter, the story is basically over. When Rainsford says, "Get ready, General Zaroff,' he obviously means "Get ready to defend yourself." And when Zaroff replies, "On guard, Rainsford," he can only mean that this is going to be a fight with swords. The term "On guard" is only used in duels with swords.
The only question is whether Rainsford has committed a crime by killing a man in a duel. That would depend on the law in the country where the duel took place. But even in a country where dueling was against the law, killing a man in a duel would not be considered "cold-blooded murder" or "first-degree murder." It sounds a lot more like self-defense, since both men are armed and seem to be equal opponents. Furthermore, Rainsford and Zaroff do not appear to be in any country but on an island that belongs to no one but Zaroff. So perhaps even Zaroff could not be considered a cold-blooded murderer, since he owns the island and makes the laws. Rainsford could not turn Zaroff over to any law-enforcement agency in a country such as Cuba or the U.S. because they would have no jurisdiction. That seems why the author opted to have Zaroff killed.
In "The Most Dangerous Game", one quote truly stands out to prove that Rainsford commited murder, and not self defense.
"The general made one of his deepest bows. "I see," he said. "Splendid! One of us is to furnish a repast for the hounds. The other will sleep in this very excellent bed. On guard, Rainsford." . . . He had never slept in a better bed, Rainsford decided."
This quote first depicts how the general had raised the white flag and decided that the game was over, Rainsford had won. However, Rainsford did not stop there and decided that it would be important to finish Zaroff rather than reporting him when he got to safer grounds. Some may argue that this was a selfless act for others taht would step into the Zaroff's home, but then Rainsford must have felt guilty about it. However, he states the he never slept easier, which leads the reader to believe that Rainsford had taken pleasure out of killing general Zaroff.