Ructions is a plural noun (informal) and means a scrap, a fracas, a disturbance or fuss. It is often used as a means of threatening dire consequences if someone misbehaves... If you don't do as you're told this moment there'll be ructions.
According to the dictionary it can also be seen as a singular noun, ruction, meaning an uproar; a noisy or quarrelsome disturbance. I'm not sure that I can recall ever hearing it used in the singular.
