THE GLIDER PILOT REPORTED THAT WHILE THERMAL SOARING AT AN ALTITUDE OF 3350 FEET, HE ENCOUNTERED SINKING AIR. HE STATED THAT HE TRIED TO RETURN TO THE DEPARTURE AIRPORT, BUT SUBSEQUENTLY HEADED FOR AN OPEN FIELD ONE-HALF MILE FROM THE AIRPORT. HOWEVER, A UTILITY POLE WAS IN HIS PATH. DURING A TURN TO AVOID THE POLE, THE GLIDER WAS REPORTED TO HAVE STALLED ABOUT 25 FEET ABOVE THE GROUND AND STRUCK THE GROUND IN A NOSE DOWN, LEFT WING LOW ATTITUDE.