The pilot reported that he was conducting takeoffs and landings in the airport traffic pattern at the time of the accident. He had completed three landings without incident. He stated that after the airplane had touched down on the fourth landing, it became airborne briefly. As it settled back down, it veered to the right and departed the runway pavement. The pilot-rated passenger reported that he was on the flight controls with the pilot "following lightly," during the accident landing. When the airplane began to roll to the right, the pilot assumed full control but was unable to avoid the runway excursion. The left main landing gear subsequently collapsed before the airplane came to rest in the grass area adjacent to the runway. The airplane sustained substantial damage to the fuselage and horizontal stabilizer. The pilot noted that a skid mark on the runway indicated that the right brake might have inadvertently been applied during the landing. He stated that there was no mechanical malfunction or failure associated with the airplane prior to the accident.