The victim, identified as a 37-year-old man, was hospitalized in critical condition with gunshot wounds to his back, abdomen and left leg, police said.
The victim had been disturbing customers in the train station, police said. He pushed the staffer to the ground and fled down stairs, but the CTA worker got up and fired shots, hitting the man, police said.
CTA said the worker was employed as a customer assistant and was not allowed to carry a firearm.