B737-800
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 640
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury; Ground Event / Encounter Other / Unknown
Flight Crew Returned To Gate; Flight Crew Took Evasive Action; General Physical Injury / Incapacitation
Equipment / Tooling; Human Factors; Procedure
During push back; the Tug Driver began shouting on the interphone; 'The plane is loose...stop the aircraft! Stop the aircraft! Stop the aircraft!' I simultaneously noticed the tug appearing in front of the nose and the aircraft picking up speed backward. I immediately stopped the aircraft by applying brakes. Apparently; the tow bar pin was not connected properly to the tug.  FAs (Flight Attendants) notified me the A FA had lost his balance and hit his head on the forward galley. We returned to the gate and contacted Operations for medical personnel to meet the aircraft. We coordinated with Dispatch for StatMD; who discussed the situation with the paramedics. FA was unsure if he wanted to go to the hospital. It was decided that he would go to get checked out. Operations supervisor was called and was to meet FA at the hospital. We had a replacement FA assigned. There was no damage to the aircraft. We departed uneventfully.
[Report narrative contained no additional information.]
B737 flight crew reported an abrupt application of the aircraft brakes and injury to a cabin crew member during pushback when the towbar became disconnected.