This is a phenomena of mob violence which has been stoked up by individuals and social media.
PSNI Chief Constable Matt Baggott added it was fortunate nobody had been killed or seriously injured last night, and he praised police for doing a "magnificent" job.
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Swapping snow for sunshine
A Red Arrows aircraft has crashed at RAF Valley, it is understood there were two people on board the jet.
Peter Pickering - who became known as the Beast of Wombwell - has been found guilty of abducting and raping a woman forty-six years ago.