Ex-UFC fighter Melvin Guillard knocked out a man on the street in Colorado while working as a bouncer for a popular bar ... and TMZ Sports has now obtained video of the violent punch.
Guillard was working for the Ginn Mill in Denver back on June 15, 2018 ... when a scuffle broke out inside of the bar.
You can see in the video, bouncers wrestle with a man to get him outside ... when suddenly, another male approaches the commotion.
That's when Guillard goes after the guy, pushing him back with one arm .