Amok Time

Spock's Condition: Spock goes through a Vulcan condition called "pon farr," making him act different.
The Challenge: Spock has to fight because of Vulcan traditions. He fights Captain Kirk, but it’s part of a Vulcan ritual, not because they are mad at each other.
T'Pring: Spock’s Vulcan bride-to-be, T'Pring, chooses Kirk as her "champion" to fight Spock.
The Fight: Kirk doesn’t want to fight but must because of Vulcan rules. After the fight, Spock thinks he killed Kirk, but it was a trick.
Ending: Kirk is fine, and they go back to the Enterprise.