I have a definition in need of a word: A universal term for a place where opponents compete. Unfortunately, most words are specific to one type of sport or combat, but I can't think of one that would apply universally.
Limited examples: Boxers fight in a boxing ring; MMA fighters have a cage or octagon. A circus act has a ring, card players have a table, cars have racetracks, punk rockers have mosh pits, and politicians have districts.
The significant constraint is that it has to be a place with a boundary or demarcation, and the only people inside these places (excluding support personnel) are the opponents.
Best Answer
You appear to be looking for an arena.