The sport pilot, was also the owner of the experimental, amateur-built, tailwheel airplane stated that he was demonstrating maneuvers for the purpose of developing his brother's familiarity with the make and model airplane. The sport pilot's brother was a pilot-rated passenger, seated in the right seat and had not previously flown the make and model airplane. After completing about 1 hour of maneuvers, the sport pilot's brother attempted a takeoff in calm wind. During the takeoff roll, as the tail became airborne, the airplane began to swerve. The sport pilot's brother overcorrected for the swerve and the airplane departed the right side of the runway. The sport pilot attempted to regain control and climb over obstacles, but the airplane stalled and impacted a field. Examination of the wreckage by a Federal Aviation Administration inspector revealed damage to both wings and the fuselage. The inspector did not observe any preimpact mechanical malfunctions, nor did the pilots report any.