In the arena, crowd members will cheer you on as you and other players fight eachother.
Maybe if someone hasn't attacked someone else after a certain time period, the crowd should throw projectiles at them. Projectiles should probably be foods like potatoes, tomatoes, etc, they don't do any harm though, but they will knock you back. But there should also be a small chance for the crowd to get so angry, that they might throw pebbles at the person who's being inactive, which can deal a little bit of harm to them.
There should be an option to turn off the crowd, or to change how long until the crowd members get angry.
Special crowd members should also appear, maybe priests that drop healing items somewhere in the arena.