The pilot of a tailwheel-equipped airplane reported that during the landing roll in gusty crosswind conditions, the airplane abruptly veered to the left because his right foot had rolled off the right rudder pedal. He further reported that he was able to regain rudder authority, but the airplane was approaching the left edge of the runway and he did not want to "apply hard right rudder" for fear of blowing a tire. Subsequently, the airplane departed the runway surface into soft grass. During the runway excursion, the right main landing gear dug into the grass, folded under the fuselage, and the airplane ground looped. The left wing sustained substantial damage. The pilot reported after the accident he found the right rudder foot pad cover had rolled off the rudder pedal and was lying on the cockpit floor. An automated weather observing system at the airport, near the time of the accident, reported the wind at 280 degrees true at 7 knots, gusting to 16 knots. The landing was on runway 26.