On May 21, 2000, at 1238 hours Pacific daylight time, a Stinson 108-1, N8398K, owned and operated by the pilot, experienced a loss of control during landing rollout on runway 12 at the Whiteman Airport, Los Angeles, California. The airplane ground looped and was substantially damaged. The airline transport pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight, which was performed under 14 CFR Part 91. The flight originated from Whiteman about 1235. The pilot reported to the National Transportation Safety Board investigator that he performed a normal landing and touched down on the runway numbers. Thereafter, his right foot slipped off the rudder pedal and his tennis shoe became wedged beneath it. Despite his efforts, he was unable to immediately dislodge his foot, and he lost control of the conventional gear airplane.