A violent stranger attacked a fellow straphanger aboard a Brooklyn subway train, chipping the victim’s tooth during the unprovoked attack, police said.

The 67-year-old victim was on a southbound L train that had just pulled into the Graham Avenue subway station in Greenpoint around 6:35 p.m. Jan. 12 when the straphanger suddenly punched him without saying a word, cops said.

The attacker quickly took off when the train doors opened.

The victim also suffered an injury to the inside of his lip and swelling and burning to his left cheek, cops said.

The suspect is described as a black man between 35 and 45 years old with a medium build. He was last seen wearing a dark blue coat, a dark blue ski cap, dark jeans and white headphones.