This is one that often features in my English classes – along with ‘why is pineapple called ananas or similar in almost all other languages but it is called pineapple in English?’
One of my students last week floated this theory:
Before when there was a fight there was no rope to separate the fighting area from the spectators so people naturally formed a circle around the fighters. This became known as a boxing ring. When they thought of putting ropes up to form a barrier it was impossible to make it in a circle so they made it in a square but kept the name.
What do you think?