A ruckus is a noisy argument or a confused, loud mess of a situation — people shouting, a fuss breaking out, a room going sideways. It is informal. You raise a ruckus, cause a ruckus, or there is a ruckus in the street. American English uses it a lot; British speakers understand it, but they also have their own cousins like row and ructions. It is not, by itself, a street fight or a riot, though a fight can start as a ruckus. It is more “what a noise and what a bother”. You would not put it in a formal letter. Teachers and parents say it when they mean stop making such a noise about this. One ruckus, two ruckuses — the singular is the form you will hear.