I lack backinfo on the video, but was told the incident happened in Shanghai, China, and involved a knife attack on school kids.
The video shows the aftermath of said knife attack. In the video, multiple kids are seen in the pool of blood on the sidewalk. Toward the end of the video, a man, presumed attacker, is shown being held pinned down on the ground.
Props to Best Gore member @xiaofuji for the video: