An arena is a large, usually circular, place where an audience can watch performances or sports competitions. We often use arena figuratively to mean any sphere or place of important activity, debate or competition, such as the political arena.
The civic centre was not big enough to hold the audience for the Prime Minister's speech, so the party rented space in a nearby sports arena. Some people will end up sitting behind the Prime Minister because of the circular shape of the room, but at least they can attend the speech.
Congresswoman Waters took several years off to raise her children and work in the private sphere. But now that her youngest daughter is in college, she is ready to get back into the political arena.
A synonym for arena as a place of debate or competition is ring, which is the place where boxers or wrestlers meet to fight. While in the arena suggests a place for debate and competition, in the ring suggests even more intense debate and conflict. To encourage a person to return to a competition after a loss or setback, we often tell them to get back in the ring.
Sarah was a great chess player. She was discouraged after losing several games, but when she was offered a place in a national competition, her friends convinced her to get back in the ring and try to play again.