The Spa Fields riots were incidents of public disorder arising out of the second of two mass meetings at Spa Fields, Islington, England on 15 November and 2 December 1816.
The meetings had been planned by a small group of revolutionary Spenceans, who invited the popular radical speaker Henry Hunt to address the crowd. They hoped that the meetings would be followed by rioting, during which they would seize control of the government by taking the Tower of London and the Bank of England. The first meeting ended peacefully, with Hunt being elected to deliver a petition to the Prince Regent, requesting electoral reform and relief from hardship and distress. At the second meeting some of the Spenceans harangued the crowd before Hunt arrived and led away a section of it. The rioters raided a gunsmith's shop and exchanged gunfire with troops at the Royal Exchange. Other incidents took place at Snow Hill and Minories, but after soldiers refused to hand over the Tower of London the rioters dispersed.
In the aftermath of the riots, four leading Spenceans, John Hooper, Thomas Preston, Arthur Thistlewood and James Watson, were arrested and charged with high treason. Watson was tried first and the chief prosecution witness was John Castle, a government spy who had infiltrated the Spenceans. Castle's evidence was discredited by defence counsel and Watson was acquitted, at which point the prosecution presented no evidence against the other defendants and all four were released.