Authorities say the officer shot the man in the leg after a dispute broke out inside the Old Gallery Sports Bar just after 4 a.m.
The dispute spilled outside, where gunfire was exchanged.
The injured man was taken to Lutheran Medical Center with non life-threatening injuries.
As many as four people were taken into custody following the shooting.
The off-duty officer was reportedly not injured.
Numerous streets were closed for the investigation. Additionally, the F subway train bypassed the 18th Avenue station in both directions for much of the morning commute.
