Padres fan brutally knocks rival MLB supporter out cold with one-punch hit – but police say victim will not press charges (VIDEO)

A baseball fan has been caught on camera clattering a rival supporter with a punch that knocked him out before he could even fall back to his seat, sending his glasses flying off his face in a fight that alerted police in the US.

The riled man can be seen casually strolling towards the victim during the Major League Baseball game between the Colorado Rockies and the San Diego Padres, calmly unleashing a brutal shot that sent the recipient swaying as he fell back apparently unconscious, losing his spectacles.

A crowd watched on as the shocking knockout played out during the sixth innings of the Rockies' win, with onlookers attempting to restrain the brawler and police swooping afterwards.

"The wildest part, to me, is that after he knocks the guy out, the Padres fan sees all the people swarming him and he just stands there," said one viewer.

"Guessing he knew what he got himself into. Seemed to take the swarm in his stride, knowing he earned it. It's baseball, folks – let's just chill out."

Several fans could be seen grappling the assailant, with some keeping him in a headlock while officers descended.

Responding to suggestions that the man behind the powerful punch could have been prosecuted for assault, Denver Police revealed that the object of his ire had refrained from potentially taking matters further.

"The person who threw the first punch was contacted by police," the authority said.

"However, the person struck did not want to press charges. No one was arrested."

That earned more assumptions and praise for the felled fan, who appeared to have regained his senses later in the clip.

"Imagine you get punched in the face – dropped, even – and you wake up and are just like, 'yeah, I don’t want to ruin this guys life over a drunken fight at a baseball game.'" said one observer. "That guy's awesome."