A brute cold-cocked and viciously assaulted a 55-year-old man while walking on the Upper West Side, cops said Tuesday.

The violent encounter unfolded just before 2:45 p.m. on Feb. 5 when the unknown attacker ran up behind the 55-year-old and hit him in the head, knocking him to the ground, according to police.

The brute then continued the beatdown, punching him and stomping on the 55-year-old as his victim writhed in pain on the ground, according to a video released by the NYPD Tuesday.

The assailant took off and is being hunted by cops.

The 55-year-old was taken to the hospital, where he was treated for wounds to his head and body before he was released, police said.

It was unclear if the pair knew one another.