Black Lives Matter (BLM) is a decentralized political and social movement protesting against incidents of police brutality and all racially motivated violence against black people. While there are specific organizations such as the Black Lives Matter Global Network that labels themselves simply as “Black Lives Matter”, the Black Lives Matter movement comprises a broad array of people and organizations. The slogan “Black Lives Matter” itself remains untrademarked by any group. The broader movement and its related organizations typically advocate against police violence toward black people as well as for various other policy changes considered to be related to black liberation.
There is no reliable source of where or when exactly this happened, but in the video, we can see people are wearing fabric masks so we can tell this event was recent.