While on takeoff from the airport in a tailwheel-equipped airplane, the pilot reported that as he applied right rudder, a muscle spasm shot through his right calf. The spasm resulted in the pilot’s foot pressing hard on the right rudder pedal. Before the pilot could regain directional control, the airplane’s tail swung left, and the airplane steered towards the runway edge. The airplane’s left main landing gear contacted a runway taxiway light collapsing the left main landing gear and the airplane settled on the left wing and ground looped. The pilot had already pulled the throttle back during the muscle spasm and the airplane skidded to a stop. The airplane sustained substantial damage to the left wing and left horizontal stabilizer. The pilot said that he felt that his lack of proper hydration led to his muscle spasm. There were no reported mechanical malfunctions or failures that contributed to the accident.