This video apparently shows the results of a ‘Knockout’ attack backfiring.
At the start the white-shirted attacked can be seen running across the screen. He runs up to a woman and hits her, overbalancing as he does so.
A bystander sees what happened and runs in quick as a flash to soccer kick the attacker into stupor while the female victim flails at the back of his head.
MMA figures such as Kenny Florian have spoken out recently against the so-called new ‘craze’, which has seen numerous unprovoked attacks on pedestrians in parts of the US as (usually teenage) attackers try and score a knockout with a surprise punch.
If there was any doubt that this was filmed in the USA, wait for near the end where somebody goes past in the background on a Segway machine. The two-wheeled electric vehicles are “pedestrian-area transport” for people who cannot walk long distances or, usually, people who just cannot be bothered walking.