The Gamesters of Triskelion

Kirk, Uhura and Chekov are set to beam down to examine and maintain a communications relay station, when they vanish from the transporter room in a way inconsistent with normal transport! They have been whisked across planetary systems by the mysterious Providers, who gather "inferior" beings from all over the galaxy and pit them against each other in blood contests. This activity is the only thing that stimulates the Providers.

Synopsis adapted from TVmaze (CC BY-SA 4.0)