The seven arenas
Each battle is fought in one of seven arenas, picked at random. Six of them are the league venues.
The venues

Training Yard Where the school trains: a plank palisade, red-and-gold bell banners and the Driftwell between the duellists. 
Mud Pit Backyard brawls behind the Dented Bell's woodshed, refereed by a hen. 
Tavern Circle A ring of stools in a Knuckleford tavern. The loser pays the round. 
Market Ring A rope ring between the fish stalls on market day. The whole town bets. 
Barge League Duels on lashed barges drifting downriver, cheered on from both banks. 
Quarry Colosseum An old granite quarry cut into terraces. The cheering echoes for a week. 
The Great Bell The most famous arena in the world, under a bronze bell as big as a house. Only champions may ring it.
How arenas are used
Every duel picks one of the seven backdrops at random, regardless of your league. The six venues double as the names of the leagues, from the Mud Pit at the bottom to the Great Bell at the top. The main menu shows a tournament day at sunset, with packed stands, bunting and the bell on the gate.
The arenas are drawn in the same pixel-art style as everything else in the game: see the art style.