On May 1, 2010, about 1852 eastern daylight time, an Interstate S1A, N34926, registered to and operated by a private individual, collided with the ground shortly after takeoff from a private airstrip in the vicinity of Lakeland, Florida. The sport pilot sustained serious injuries, and the airplane was substantially damaged. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight operated under the provisions of 14 Code of Federal Regulations, Part 91. The flight was originating at the time of the accident. A witness located at the private airstrip observed the airplane climb to approximately 500 feet after takeoff. She reported that as the airplane was turning to the left, the nose of the airplane “dived”, and the airplane descended rapidly. She stated that as the airplane descended toward the ground, the pilot pulled up at the last few seconds, clipped a tree, and landed hard in a field. The airplane continued to travel forward through a fence and across a dirt road, where it nosed over and came to rest inverted. Examination of the airplane by a Federal Aviation Administration inspector revealed that the airplane impacted a grass field. Three large propeller strikes were observed along the ground scar. Flight control continuity was established to all flight control surfaces and flight control system components revealed no evidence of preimpact mechanical malfunction. Examination of the fuel system revealed an undetermined amount of fuel remained in the fuel tanks. No water or debris was found in the fuel system. Examination of the engine revealed valve train continuity, compression, and spark from the magneto leads. The examination of the engine and system components revealed no evidence of preimpact mechanical malfunctions. The NTSB investigator-in-charge did not receive NTSB Form 6120.1, Pilot/Operator Report from the pilot.