This footage comes from the records of the secret police, who monitored a demonstration in Prague on 21 August 1989.
In Czechoslovakia, the protests against the regime were smaller than in neighbouring countries. By the summer of 1989, a new multiparty government had emerged in Poland, and the Iron Curtain had collapsed in Hungary. Inspired by this situation, people in Czechoslovakia took action, and the demonstrations on the anniversary of the Soviet occupation in 1968 were already large. In Prague, about 2,000 people demonstrated and demonstrations were also held in other cities. The police and other security forces tried to dispel them. In the clip, it may seem that the police were in the minority. We see a young man from the clip The Kid and the Housekeeper, whom policeman are attacking. Gradually, however, the police forcibly ended the demonstration and arrested over 150 people, many of them foreigners.
The violent confrontation on both sides showed that the situation in Czechoslovakia, after the quiet period of normalisation, had begun to unravel. A few months later, on 17 November 1989, a student demonstration was brutally dispersed. The police intervention caused an argument that escalated into mass protests leading to the fall of the communist regime in late 1989.