Around 8:30 p.m., the victim was on a train car near 63rd St. when a verbal altercation ensured with four other individuals. One of the individuals then pulled out a gun and fired shots.
The victim was struck twice in the stomach, police said. He was transported to an area hospital in critical condition.
No one is in custody as Area One Detectives investigate.
Trains were temporarily suspended between 95th and 47th Streets due to police activity, according to a tweet from CTA.
No further details were immediately available.