THE PILOT REPORTED THAT AS HE WAS BACK-TAXIING ON THE RUNWAY, AN ABRUPT LEFT TURN WAS INITIATED AS THE PILOT FIRMLY PRESSED THE LEFT BRAKE. THE AIRPLANE BEGAN TO GROUND LOOP AND THE NOSE WENT DOWN. THE AIRPLANE CONTINUED TO NOSE OVER AND CAME TO REST INVERTED. THE PILOT STATED THAT HIS ATTENTION WAS DIVERTED FROM LOOKING OUT THE FRONT OF THE AIRPLANE TO LOOKING OUT THE SIDE WINDOW FOR CHUCK HOLES. THE PILOT WAS NOT AWARE THAT THE TAIL WAS COMING UP UNTIL THE AIRPLANE WAS IN THE PROCESS OF NOSING OVER.