The suspect was one of a group of street performers aboard the southbound E train near Queens Plaza shortly before 2 p.m. on Sept. 24, police said.
When a 55-year-old straphanger took out his phone and started to film the group, the suspect approached him and told him to stop recording, then punched him in the face and spit on him, police said.
The suspect ran off the train at the Queens Plaza station, police said, leaving the man with a cut on the lip.
Police described the suspect as being about 18 to 25 years old, standing between 5-foot-8 and 5-foot-10 and weighting about 160 pounds.
He has black hair, brown eyes, a thin build and was wearing a Chicago Bulls hat, white T-shirt, black sweatpants and red sneakers, according to police.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 800-577-TIPS.