An injured fan is helped by a riot policeman during clashes between Red Star Belgrade and Partizan Belgrade fans in the stadium before the teams' Serbian Superliga soccer match in Belgrade, April 25, 2015. Serbian league leaders Partizan Belgrade held champions and bitter city foes Red Star to a 0-0 draw in a derby match marred by bad crowd trouble before kickoff on Saturday. The start was delayed for 45 minutes after home Red Star supporters pelted riot police with seats and flares, forcing officers to retreat from the north tier that houses the club's diehard fans. (Photo by Marko Djurica/Reuters)

Riot police officers in position to crack down on demonstrators during a protest against Venezuelan President Nicolas Maduro, in Caracas on April 20, 2017. Venezuelan riot police fired tear gas Thursday at groups of protesters seeking to oust President Nicolas Maduro, who have vowed new mass marches after a day of deadly unrest. Police in western Caracas broke up scores of opposition protesters trying to join a larger march, though there was no immediate repeat of Wednesday's violent clashes, which left three people dead. (Photo by Juan Barreto/AFP Photo)

A Palestinian demonstrator jumps in the air during clashes with Israeli riot police on May 13, 2011 in the East Jerusalem neighbourhood of Issawiya, Israel. Palestinians began marking the “Nakba” or “catastrophe” which befell them following Israel's establishment in 1948. (Photo by Uriel Sinai/Getty Images)

People lay flowers for and mourn the anti-government protesters who were killed in the past weeks’ clashes with riot police.

Riot police stood by the gates of parliament in Nairobi, Kenya, Tuesday, May 14, 2013, during a demonstration against members of parliament who demanded higher wages. Demonstrators released two dozen piglets and poured blood on the pavement to protest the demands for a wage hike. (Photo by Carl de Souza/AFP Photo)

A demonstrator dressed as Santa Claus holds up a flag as a riot police vehicle releases a jet of water during a protest against the private system of pension fund administrators in Santiago, Chile, December 10, 2015. The flag reads “Classist Workers Union”. (Photo by Ivan Alvarado/Reuters)

An anti-government protester wearing a Guy Fawkes mask stands with a shield near flames from molotov cocktails thrown at a water cannon by anti-government protesters during riots in Caracas in this April 20, 2014 file photo. (Photo by Jorge Silva/Reuters)

People take cover as riot police use pepper spray projectile during a protest as a second reading of a controversial national anthem law takes place in Hong Kong, China on May 27, 2020. (Photo by Tyrone Siu/Reuters)