The fighting area for participants in a combat sport. Origianally, these sports took place in a circle. When support ropes were added to clearer identify the border, the rings were made sqaure or rectangular in shape.
See also ring, boxing ring, wrestling ring, enter the ring, queensbury
As these two competitors enter the sqaured circle, they begin to realise that for one of them, fame and fortune on a tremedous scale awaits after this bout.