Pat Camden, a spokesman for the police union, said the officers were responding to a call of shots fired at a South Side park.
Upon arrival, police found two armed men. An 18-year-old male victim was on the ground.
Police pursued the suspects, who exchanged gunfire with the officers, Camden said.
No one was hit, and officers took the two suspects into custody.
The victim was transported to Stroger Hospital in critical condition.
Several people are being questioned as a part of the investigation.
Camden said the incident, which happened at about 4:30 p.m., is gang-related.