According to the backinfo I got, this happened in Puerto Rico. The two shirtless guys reportedly spent the night drinking together, but the booze got the best of them both and after a night of being best drinking pals, they ended it by turning on each other.
Prior to the altercation in the video, the guy who got chair-pushed had pulled out a knife on his drinking buddy. That escalated into what we see in the video.
The chairman (props to Best Gore member @natural-selection-2 for that one – well done), originally using the chair as a defense shield, tossed it at the knifeman which knocked his unstable drunk ass down, where he got double tapped by the pavement. The chairman then picked up the knife and appears to stab the knocked out chap with it.
That prompted some local guy to pick up the chair, and assault the leaving chairman with it from the back. Luckily he went down directly under a pharmacy sign… so painkillers are not far away.
Many thanks for the video @natural-selection-2: