Why do you think a boxing RING is SQUARE?

Initially, it would have been a ring but a square would serve much interest of the manufacturers of the arena as it is always easy to build a square structure than a circular structure. Also the seating arrangements and everything will have to match the circle. In a small boxing ring, it would not be cost effective but for a stadium, it will be cost effective too.

A word of Caution - Above statement is author's own perception and prejudice.

They used to be round but the referee had difficulty sending the boxers back to their corners lol

To have a corner to hide in...

Interestingly, i believe a sumo wrestling ring is not square.

A square is easier to make than a circle

Cuz ya need to have a place to get on when you do a cool jump move!

I’m wrestling it’s called the squared circle

Good question.