From Amazon.com
"Arena" was based on a script by
Trek producer Gene L. Coon, the other indispensable figure (besides Gene Roddenberry) in making
Star Trek what it was. After writing what he believed was an original teleplay about a one-on-one battle between Captain Kirk (William Shatner) and the reptilian commander of an enemy vessel, Coon realized he had probably been subconsciously inspired by a similar short story written by Fredric Brown (who was promptly credited and paid). The concept of a human-and-alien duel to the death in primitive terrain, however, was slightly ubiquitous in the 1960s (see "Fun and Games," a masterpiece from the original
Outer Limits TV show) and was revisited in the '80s via the Arnold Schwarzenegger feature
Predator. But under Coon's guidance and direction by Joseph Pevney, "Arena" stands on its own as a particularly strong story of what battle does to one's humanity. Shatner is in great form for this one.
--Tom Keogh
From the Back Cover
While pursuing a ship that destroyed a Starfleet base, Kirk intrudes into the territory of the highly advanced Metrons, who decide to settle the conflict.
TREK TRIVIA
Most of this episode was shot on location at Vazquez Rocks and featured the fort that had been used in "The Cage."
"Arena" marked the first use of a Universal Translator. The voice of the Metron was provided by Vic Perrin, who supplied the voice of the "baby" Balok in "The Corbomite Maneuver."