Today when you think of a tournament you think of things like sports playoffs or activity that has a group of people competing until only one is left.
Waaaaayyy back in the times of knights and heirs, a tournament was a mock battle fought by knights. They were usually divided into two sides, using blunted or wooden weapons. One of the major skills they needed to possess was the ability to command their horse using only their knees. Their hands would be full of weapons, shields and such. So prior to the “battle” each knight was tested on his horsemanship by guiding his horse through a maze of wooden poles while holding his arms up at shoulder height. If he could “turn” his horse skillfully enough, he could participate. The French word for turn is tourner, and thus the phrase “tournament” was born.