THE HELICOPTER WAS ON A FLT TO TRANSPORT AN ACUTELY ILL PATIENT FROM ONE HOSPITAL TO ANOTHER. THE AIRCREW CONSISTED OF A PLT & TWO FLT NURSES. DURING ARRIVAL AT THE DESTINATION, THE PLT BEGAN AN APCH TO AN ATHLETIC FIELD THAT WAS SURROUNDED BY TALL BLDGS & A POWER LINE. THE PLT SAID THE APCH WAS MADE ON A SOUTHEASTERLY HEADING WITH THE WIND FROM 230 DEG AT 7 KTS. AT ABOUT 45 FT AGL WITH AN AIRSPEED OF APRX 25 KTS, TRANSLATIONAL LIFT WAS LOST & THE HELICOPTER YAWED LEFT. THE APPLICATION OF FULL RIGHT ANTI-TORQUE PEDAL FAILED TO STOP THE YAW. THE HELICOPTER TOUCHED DOWN IN A LEFT YAW & THE PLT APPLIED COLLECTIVE. IT BECAME AIRBORNE AGAIN, STILL IN A LEFT YAW, THEN THE NOSE GEAR STRUCK THE GROUND & THE ROTOR BLADES STRUCK A BRICK WALL OF A BUILDING ON THE SOUTH SIDE OF THE FIELD. AN EXAM OF THE WRECKAGE REVEALED NO PREIMPACT DESCREPANCIES. THE FLT NURSES REPORTED THAT THE APCH SEEMED HIGHER & FASTER THAN NORMAL. APRX 7 MI NNW AT PITTSBURG, PA, THE WIND WAS FROM 260 DEG AT 10 KTS. THE PLT HAD APRX 30 HRS WITH CLOCKWISE/FRENCH ROTOR SYS.