DURING INITIAL CLIMB THE AIRCRAFT WAS OBSERVED AT A HIGH ANGLE OF ATTACK AT LOW ALTITUDE BEFORE DESCENDING IN A STALL/SPIN COLLISION WITH THE GROUND. WITNESSES AT THE APRT REPORTED THAT THE ENGINE SOUNDED ROUGH DURING THE TAXI AND TAKEOFF ROLL. THE PLT HAD RECENTLY PURCHASED THE EXPERIMENTAL HOMEBUILT ACFT AND SEVERAL WEEKS BEFORE THE ACCIDENT HAD ATTEMPTED TO LAND THE TAIL-WHEEL ACFT FOR THE FIRST TIME. THE PLT HAD NO PRIOR TAIL-WHEEL EXPERIENCE. THE ACFT GROUND LOOPED CAUSING SUBSTANTIAL LANDING GEAR DAMAGE AND SUDDEN STOPPAGE OF THE ENGINE. THERE WAS NO RECORDED MAINTENANCE PERFORMED ON THE ENGINE SINCE THE INCIDENT. THE ACCIDENT FLIGHT WAS THE FIRST FLIGHT ON THE ACFT SINCE THE INCIDENT AND THE PLT'S SECOND FLIGHT IN THE ACFT. THE CAUSE OF THE LOSS OF POWER WAS NOT DETERMINED. THERE WAS NO EVIDENCE OF CONTROL SYSTEM MALFUNCTION.