Trial by combat
Trial by combat was method of law that allowed someone who was accused of a crime to fight another person for their freedom rather than standing trial. However if the accused didn't win the fight, then the accused would be put to death.
On Gelrak V, the natives practiced this method when the away team from the USS Cerritos was captured for offending the natives with a gift suitable for their enemies. Commander Jack Ransom fought Vindor their champion and defeated him, and they were all subsequently set free.
After this had occurred, Gernba, the leader of the planet, realized that his people would have to cease the use of trial by combat. Vindor suggested that they have an actual trial with a judge. But Gernba instead decided that they would do a death race instead. (LD: "Temporal Edict")