The July 1944 issue of Astounding Science Fiction included the story "Arena," by Frederic Brown. The human race and an invading alien race are about to have it out in a massive space battle. An all-powerful advanced alien, knowing the battle will effectively doom both races, opts to intervene. He drops a human and an alien into a sort-of arena, surrounded by a force field. He tells them to fight to the death. The loser's entire race will then be obliterated. Thus, at least one of the races will survive.
The story is pretty cool, with both the human and the alien improvising weapons while trying to figure out a key aspect of their new environment. In the end, the human may have deduced something that will give him just enough of an advantage to win. But his plan includes the necessity of smacking himself unconscious with a rock, so his victory is far from certain.
Trust me. It all makes sense when you read the story. Try to track down a copy. If you have a Kindle or Kindle app, it's available in this collection.
Now let's jump ahead a couple of decades. Star Trek Writer/producer Gene L. Coon comes up with an idea in which the Enterprise encounters an alien race known as the Gorn. It looks like war between the two species, but a super-powerful alien race intervenes. They teleport Captain Kirk and the Gorn onto an uninhabited planet, where the two must battle it out for the fates of their respective species.
Coon came up with the idea on his own, but someone noticed the similarity to Brown's story. So Brown was contacted and, in the end, given a story credit. The episode, by the way, is also titled "Arena," telecast in early 1967.
You just can't keep a good idea down. The idea of two opponents being forced to fight for their entire species is a pretty cool one--the ultimate in gladiatorial combat. It's really not surprising that two writers might come up with the same idea.
Or is it three writers? Three years before Star Trek, Outer Limits did a very similar story:
It seems you REALLY can't keep a good idea down.