Short answers, pulled from the story.
Riot is a statutory offence in England and Wales created by section 1(1) of the Public Order Act 1986. A single person can be liable for an offence of riot when they use violence provided that it is shown there were at least twelve present using or threatening unlawful violence.
Tin miners plundered granaries at Falmouth in 1727. Food riots may occur due to food shortages caused by harvest failures, incompetent food storage, hoarding, poisoning of food, or attacks by pests like locusts.
During the 1992 Los Angeles riots, 63 people were killed and over 700 businesses burned. Property damage was estimated at over $1 billion and more than 12,000 people were arrested.
Police may use less-than-lethal methods of control such as shotguns that fire flexible baton rounds or rubber bullets to injure or otherwise incapacitate rioters. This allows them to break up a riot or allow easier arrest.
In a race riot, race or ethnicity is the key factor while the term entered the English language in the United States by the 1890s. In a religious riot, religion is the key factor and historically these involved groups arguing who possesses the primate of orthodoxy.