rioter

Concise Oxford English Dictionary © 2008 Oxford University Press:
riot/ˈrʌɪət/

▶noun

• 1 a violent disturbance of the peace by a crowd.

  ■ archaic rowdy behaviour.

• 2 an impressively varied or lavish display: a riot of colour.

• 3 (a riot) informal a highly amusing or entertaining person or thing.

▶verb

• 1 take part in a riot.

• 2 behave in an unrestrained way.

• 3 archaic act in a dissipated way.

– phrases
read someone the Riot Act give someone a severe warning or reprimand. [from the name of a former act partly read out to disperse rioters.]
run riot

• 1 behave or be displayed in a violent and unrestrained way.

• 2 proliferate or spread uncontrollably.

– derivatives
rioter noun.

– origin ME: from OFr. riote ‘debate’, from rioter ‘to quarrel’, of unknown ultimate origin.