B727 CAPT RELEASED ACFT BRAKES. ACFT MOVED. TOWBAR INJURED CGP.

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I WAS THE FO ON A PART 121 TURBOJET (B727) FLT FROM BILLINGS TO DENVER. OUR PROCS REQUIRE THAT IF LNDG IS TO BE MADE OVER A CERTAIN WT AND DENSITY ALT; 'MAX QUICKTURN' PROCS APPLY; MEANING THAT AFTER CONSULTING OUR FLT MANUAL CHARTS; EITHER MAINT HAS TO CHK THE TIRE TEMPS WITH PARKING BRAKE RELEASED OR 44 MINS MUST ELAPSE TO THE NEXT TKOF. AS WE PULLED INTO THE GATE; OUR MARSHALLER SIGNALED US IN; BUT NEVER GAVE US THE 'ACFT RECEIPT COMPLETE' THUMBS UP SIGN. AS WE NEEDED TO RELEASE OUR BRAKE (MAINT WAS INFORMED) WE (CAPT AND I) ATTEMPTED TO GET HIS OR ANOTHER MECH'S ATTN; EITHER WITH THE GND CREW HORN OR FLASHING THE TAXI LIGHT 3 TIMES. NO LUCK GETTING HIS ATTN AS WE CONTINUED TO HOLD THE BRAKES. ANOTHER MECH NOTICED OUR ATTEMPTS TO GAIN THE FIRST ONE'S ATTN; WALKED UP TO THE R FORWARD SIDE OF THE ACFT AND SIGNALED TO US 'CHOCKS IN;' 'RELEASE BRAKES' AND 'THUMBS UP.' SEEING THIS; THE CAPT RELEASED THE BRAKES. AS ONLY THE L CHOCK WAS IN; THE ACFT ROLLED SLIGHTLY REARWARD AND THIS MOVEMENT CAUSED THE TOWBAR; WHICH WAS RESTING NOW ON THE NOSE GEAR; TO FALL ON THE FIRST MECH'S FOOT. THE FIRST MECH HAD TO RPT TO MEDICAL. HE DID SAY; HOWEVER; THAT HE DIDN'T TELL THE SECOND MECH TO SIGNAL US TO RELEASE THE BRAKES. SUPPLEMENTAL INFO FROM ACN 414124: THE QUICKTURN WT WAS EXCEEDED; THEREFORE; WE WERE REQUIRED TO RELEASE THE PARKING BRAKE AFTER WE WERE PARKED AT THE GATE. THE GUIDEMAN SIGNALED US TO STOP AT THE GATE AND PARKING CHKLIST WAS COMPLETED. SHORTLY THEREAFTER; I ATTEMPTED TO CONTACT THE MECH WHO PARKED US TO DETERMINE IF THE ACFT WAS CHOCKED AND WE WERE CLR TO RELEASE BRAKES. HE WAS UNRESPONSIVE. I FLASHED TO TAXI LIGHT AND ANOTHER MECH APCHED THE ACFT. I GAVE THE HAND SIGNAL FOR 'CHOCKS IN' AND HE RESPONDED WITH THE CHOCKS IN SIGNAL FOLLOWED IMMEDIATELY WITH A RELEASE BRAKES SIGNAL AND A 'THUMBS UP.' I THEN RELEASED THE BRAKES AND THE ACFT ROLLED SLIGHTLY AFT. SHORTLY THEREAFTER THE ORIGINAL MECH CAME INTO THE COCKPIT AND SAID THE TOWBAR HIT HIM ON THE FOOT. UPON INSPECTION OF THE NOSE GEAR I NOTED THAT ONE END OF THE TOWBAR WAS ATTACHED TO THE ACFT AND THE OTHER WAS FREE. ALSO; ONLY THE L NOSEWHEEL WAS CHOCKED WHICH CAUSED A TURNING MOMENT TO THE R AS THE ACFT ROLLED AFT. PERHAPS IF BOTH WHEELS HAD BEEN CHOCKED; THIS EVENT WOULD NOT HAVE OCCURRED.