There is one story that has a plot similar to The Outer Limits' Fun & Games, & a slight resemblence to Star Trek's The Arena, and might be "based upon a story by Robert Specht (from his original teleplay entitled 'Natural Selection'", just as is Fun & Games.
Anyway, here is the synopsis of the 97th Episode: Confrontation in Space (December 5, 1964)
Planet Hyper is the most civilized planet in the galactic system. Now it chooses a pair of a human and a robot each from both the Earth and Planet War to have them fight against each other, and decides to destroy the loser's planet. Atom and Ponkotsu Tetsu, the safebreaker, are chosen to represent the Earth.
Here is a quote from Fun & Games:
A former boxer, now a part-time hood, named Mike Benson (Nick Adams) and a woman just coming from out of a troubled marriage named Laura Hanley (Nancy Malone) are quite bewildered when they are unexpectedly "electroported" away from Earth and find themselves inside a foggy, otherworldly room...
They are to engage in a battle of wits and survival with another alien race upon the Anderans' especially selected arena planet in order to entertain the bloody-minded masses of Anderan. Making matters worse, the losers' home world is to destroyed in the contest's aftermath.
Similarity very high. The page for Fun & Games notes the similarity to Star Trek's The Arena, & after seeing both Fun & Games & the Arena, I noted a very great similarity between the aliens pitted against the Earthilings, both were lizard-men.
Here is a quote from The Arena:
Without warning, Kirk finds himself alone on the surface of a harsh desert planet. Alone except for the Captain of the alien Marauder, a hulking reptillian humanoid of the Gorn species. The Metrons have decided on "trial by combat" to solve the dispute. Kirk and the Gorn captain must battle to the death...the survivor's ship will be allowed to depart. The loser will be obliterated. And so, stranded on an unknown world, with only natural resources to rely on, Kirk must battle the much stronger and more ferocious Gorn, with the lives of his whole crew on the line.
Outer Limits' Calco
Star Trek's Gorn
Hopefully, TRSI will soon restore this episode, it would be funny if Astroboy'sopponent is also a lizard-man.
Anyway, all 192 episodes are briefly discribed on this page , which is found here [url=http://en-f.tezuka.co.jp/anime/sakuhin/ts/ts002.html]Animation Works: Astroboy under the Subtitles
A good many of these draw their stories from the manga,