In Beowulf, what is the conflict in The Battle With Grendel?

I think this question might be asking about a conflict type. If that is the case, then the epic battle that occurs between Beowulf and Grendel is a man vs. man conflict. It is also conceivably possible to list this conflict as a man vs. supernatural conflict. That would only be the case if you consider Grendel as some kind of demon creature from Hell. Personally, I do not support that depiction of Grendel. I think he is a man. I didn't always think that; I initially pictured Grendel as a swamp monster of sorts with scales and spikes, but I don't think that fits the description that we are given.

Grendel, who haunted the moors, the wild Marshes, and made his home in a hell Not hell but earth. He was spawned in that slime, Conceived by a pair of those monsters born Of Cain, murderous creatures banished By God, punished forever for the crime Of Abel's death.

We are told that he is a descendant of Cain, and Cain was a human from the Bible that was guilty of fratricide. All of Cain's descendants would then have the mark of Cain upon them. We don't know what the mark is, but clearly Grendel has it, and clearly Grendel is evil. He's a cannibalistic psychopath that loves violence and killing for the sake of violence. The conflict is a man vs. man conflict because it involves a physical fight to the death between two men, and symbolically it is a good vs. evil conflict as well. Beowulf is good and pure, and Grendel is evil and tainted.

"The Battle with Grendel" is an excerpt of the Anglo-Saxon epic poem, Beowulf. This excerpt relates the events of Beowulf's fight against the monster, Grendel, who had been terrorizing the Danes and their King, Horthgar, for ten years. On the surface, the conflict is between hero and monster, and Beowulf's victory serves to win glory and renown, both for himself and for his king, as well as to pay Hrothgar back for aid the King of the Danes had rendered to Beowulf's father.
Often, however, readers find a deeper conflict within the fight between hero and monster. One common conflict attributed to the fight is the conflict of good against evil. This view finds that Grendel represents evil itself and Beowulf, as the hero, represents the constant battle of good against evil.
Another way of looking at the good against evil conflict is to frame it as virtue against sin. In this understanding of the conflict, Grendel represents the sin and vices of humankind (a claim often supported by reference to the poem associating Grendel with the descendants of Cain). Beowulf, the virtuous warrior, who, even though he is not portrayed as overtly Christian in the poem, represents many Christian ideals, represents the battle of a person against those vices and sins.
Other readers have read the conflict not as good/virtue against evil/sin, but as human against nature. In this reading, Beowulf represents the advancement of civilization, and his fight is against savage nature itself. Grendel, with his animalistic tendencies and appearance, must be subdued in order for humanity to assert itself.
It is worth noting that J.R.R. Tolkien, in his essay "Beowulf: The Monsters and the Critics," argues that the allegorical readings of the poem, and the deeper meanings given to the conflicts with the monsters, are scholarly overlays. Tolkien's position is that the poem is about human beings "at war with the hostile world, and [their] inevitable overthrow in Time." The battles against the monsters are, in effect, an outgrowth of the human will to survive even in the face of the inevitability of death.