The exact context of this video isn't known, but the footage speaks for itself. A police officer has his gun drawn on a non compliant subject. Suddenly, backup arrives to assist the officer, but the resisting subject exhibits no situational awareness and pays the other officers no mind.

One of the backup officers is able to walk right up behind the man and with a solid, sweeping kick, knocks the mans feet out from under him, sending his face directly to the paved surface. Either due to unconsciousness or a sudden moment of mental clarity, the man is taken into custody with the further resistance.