Horrific footage captures the victim walking towards a car park when a total stranger runs up behind him and launches a savage blow without warning.
The man is knocked out cold instantly and is seen flying into the concrete ground with a painful thud.
The sickening force of the punch causes the victim’s baseball cap to fly off.
Another man, in a green T-shirt, is seen running into shot as the man who has been punched lies unconscious on the floor.
But instead of helping the victim, he merely holds his arms out and appears to be smiling as the attacker walks away.
The 30-year-old victim is left KO’d in the street as onlookers walk away in the chilling clip released by police.
After spending several nights in hospital, the man is still recovering from his injuries after the unprovoked punch in Rosenberg, Texas.
Police named Alejandro Maldonado, 18, as a suspect in a post entitled “Tough guy wanted for Aggravated Assault” online.
Lieutenant Chad Pino said the victim did not know his attacker, who may have been trying to impress friends on social media.
“You think it’s a game, your friends might peer pressure you into doing something, and it’s a serious offense, it’s a felony,” he said.
“It’s an aggravated assault.
“In this case, he sustained some serious injuries and it’s not a game.
“It’s not going to be funny when you’re in prison.”
Maldonado had initially been tracked down and was cooperating with police but he cut off communication last week.
Police now hope releasing the video will shame him into turning himself in.
A number of one-punch attacks have been linked to a so-called “Knockout Game” trend in recent years.
A 37-year-old street cleaner was punched unconscious at random in Paterson, New Jersey, in 2015, in a video which surfaced on Facebook.
Kristian Gonzalez, who was aged 17 at the time, was later jailed for three years.