The airplane veered to the left and off runway 02 (5,000 feet by 100 feet, grooved asphalt) at the Dayton-Wright Brothers Airport, Dayton, Ohio, after the tail wheel touched down during landing. The pilot stated the tail wheel lock pin did not remain in the locked position. The right main landing gear collapsed and the right wing skin became wrinkled when it contacted the ground resulting in substantial damage. The pilot and three passengers were uninjured. Inspection of the tail wheel by the Federal Aviation Administration revealed no mechanical anomalies that would have precluded normal operation.