On May 22, 1999, at 1430 hours Pacific daylight time, an Aerotek Pitts Special S-1S, N93J, ground looped on landing at the Merced, California, airport. The aircraft, owned and operated by the pilot, sustained substantial damage. The commercial pilot was seriously injured. The local area personal flight originated at the Merced airport about 1400, and was conducted under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that he was practicing touch-and-go landings to runway 30. He stated that on the last landing the aircraft landed hard and bounced. He decided to do a go-around and added power. The pilot reported that the power came up and the engine sounded normal; however, the aircraft didn't climb. The airplane then veered about 10 to 20 degrees to the left. The pilot stated that he realized something was wrong and cut the power. The wingtips and propeller impacted the ground and the aircraft came to rest upright about 150 feet northwest of the 1,000-foot runway marker. The pilot reported that he has no memory of the events following the reduction of power until another person arrived at the accident site. There were no witnesses to the accident; however, another pilot heard the crash and helped the pilot egress from the aircraft. The winds were reported to be variable at 4 knots at the time of the accident.