FAILURE TO PROPERLY SECURE THE TOW BAR PRIOR TO PUSH RESULTS IN B737 FLT CREW MAKING EMERGENCY STOP WHILE ROLLING BACKWARD. FLT ATTENDANTS ARE INJURED.

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MY CREW AND I ARRIVED AT THE GATE 30 MINS PRIOR TO THE SCHEDULED DEP TIME TO FLY FROM ZZZ. WE WERE INFORMED THAT THIS FLT WAS STARTING LATE DUE TO AN ACFT SWAP. THE ACFT WE WERE RECEIVING NEEDED AN INSPECTION FOR A TRANSITORY OVERSPEED TO MACH .84 ON THE PREVIOUS FLT. I WAS BRIEFED BY THE PREVIOUS CAPT AND ALSO BY THE COMPANY MECHS IN ZZZ THAT THE INSPECTION WOULD TAKE BTWN 1-2 HRS TO COMPLETE. WHEN THE INSPECTION WAS COMPLETED; THE OUTBOUND PAX AND BAGGAGE WERE LOADED; WE STARTED OUR PUSHBACK APPROX 1 1/2 HRS LATE. THE PUSHBACK STARTED OUT VERY ROUTINELY; HOWEVER; AFTER PUSHING BACK APPROX 30 FT; THE TUG DRIVER FRANTICALLY EXCLAIMED THROUGH THE FLT INTERPHONE 'HIT THE BRAKES; HIT THE BRAKES; HIT THE BRAKES!' I ABRUPTLY APPLIED THE BRAKES AND STOPPED THE ACFT. AFTER STOPPING THE ACFT I QUERIED THE TUG DRIVER; 'WHAT IS THE PROB? WHAT ARE YOU DOING?' HE INFORMED ME THAT THE TOW BAR HAD SEPARATED FROM THE TUG (IT DID NOT BREAK) DURING THE PUSH AND AS HE ATTEMPTED TO CTL THE TUG TO STOP THE ACFT; THE ACFT CONTINUED TO DRIFT BACKWARD (UN-TETHERED) AND WAS IN DANGER OF DEPARTING THE RAMP SURFACE INTO THE TXWY LIGHTS AND GRASSY MEDIAN BEHIND THE GATE. AT THIS POINT I WAS CALLED BY THE FLT ATTENDANTS AND WAS INFORMED THAT 2 OF THE FLT ATTENDANTS WERE THROWN OFF BAL AND WERE INJURED AS A RESULT OF THE ABRUPT STOP. I COMMUNICATED TO THE FLT ATTENDANTS THAT WE'RE GOING BACK IN TO THE GATE. I DIRECTED THE FO TO INFORM ZZZ OPS AND MAINT OF THE EVENT. THE ACFT WAS TOWED BACK TO THE GATE AND THE INJURED FLT ATTENDANTS WERE DEPLANED. PARAMEDICS WERE SUMMONED TO ATTEND TO THE INJURED FLT ATTENDANTS WHILE DISPATCH AND THE CHIEF PLT ON DUTY WERE NOTIFIED AND BRIEFED ON THE INCIDENT. ZZZ MAINT INSPECTED THE ACFT AND DETERMINED THAT NO ACFT DAMAGE WAS SUSTAINED IN THIS INCIDENT. AN ACFT LOGBOOK ENTRY WAS MADE AND SIGNED OFF BY ZZZ MAINT. THERE WERE NO OTHER FLT ATTENDANTS IMMEDIATELY AVAILABLE. AFTER COORDINATING WITH DISPATCH; THE CHIEF PLT ON DUTY; AND INFLT SCHEDULING; 3 OTHER FLT ATTENDANTS WERE REASSIGNED FROM THEIR FLT UPON ARR AT ZZZ. WE ULTIMATELY PUSHED BACK APPROX 2.5 HRS AFTER THE ORIGINALLY SCHEDULED DEP TIME AND PROCEEDED UNEVENTFULLY. I SPOKE WITH THE TUG DRIVER ABOUT THIS INCIDENT AND HE ADMITTED THAT HE WAS TRYING TO HURRY THE LOADING PROCESS OF THE ACFT; FELT RUSHED; AND INADVERTENTLY OMITTED PLACING THE PIN IN THE TOW BAR WHERE IT CONNECTS TO THE TUG. WHEN HE SAW THE ACFT DRIFTING BACK UNCTLED HE BECAME VERY AGITATED AND CONCERNED THAT ACFT WOULD SUSTAIN DAMAGE IF IT WERE NOT STOPPED IMMEDIATELY. I HAVE SPOKEN TO OTHER PLTS ABOUT SIMILAR INCIDENTS OCCURRING. ALTHOUGH RARE; I STRONGLY FEEL THAT GND OPS NEED TO BE FURTHER STANDARDIZED TO INCLUDE A CHKLIST AND CHALLENGE/RESPONSE ITEM PRIOR TO PUSHBACK. SUPPLEMENTAL INFO FROM ACN 762408: THE CAPT APPLIED THE BRAKES TO STOP THE ACFT. AS A RESULT THE NOSE GEAR CAME OFF THE GND THEN DROPPED BACK DOWN.