On July 31, 1999, approximately 1000 mountain daylight time, a Piper PA-18-150, N6741L, registered to and being flown by a private pilot, was substantially damaged during a collision with a tree following a loss of control on takeoff at the Big Creek airstrip, Big Creek, Idaho. The pilot and passenger were uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was personal, was to have been operated under 14CFR91, and was destined for Caldwell, Idaho. The pilot reported that "I began my take off from Big Creek by lining up on the right side of the runway. A Super Cub was taking off in front of me on the left side of the runway. After the Super Cub departed I began my takeoff roll. The airplane pitched to the left greater than ever before. I applied right rudder and right brake. The airplane returned to the center of the runway and as I continued to apply power I released the drag on the right brake. As I released the brake the airplane pitched hard to the left towards some small trees. It felt like the left brake was locked. As I was heading to the left, I felt I was going to hit a small tree head on. I did not want to hit the tree head on so I added hard left rudder as the airplane started to ground loop. I hit the tree on the right side to the airplane and spun around to the left and stopped. I would estimate my entire take off roll of about 150 to 200 feet." He further reported that "I was departing Big Creek for Caldwell after having breakfast. I had told my passenger that their [sic] was leg room on the side of my seat. I cautioned about the rudder pedals but I did not warn about hitting the brake pedals under my seat. After I released the right brake it felt like the left wheel was locked" and that "I examined the left wheel and brake after I exited the airplane and it appeared to be normal. On the grass strip you could see where I had hard right braking in an attempt to abort the takeoff. I believe my passenger may have been resting a foot against the left brake pedal without knowing it." (refer to attached NTSB Form 6120.1/2) A pilot witness at the Big Creek airport, who was in a partial position to observe both departing aircraft, reported that he "could see both of the a/c ready for t/o, and heard the first apply power. About the time that the first a/c rotate[d] & was visible flying, the second a/c applied power. The a/c disappeared from view and then there was the sound of a concussion, the engine stopping and a large cloud of dust rising from the west end off of the strip." He further reported that "the other super cub, which had taken off first, returned & landed & taxied up near the wreckage." (refer to attached statement) An inspector from the Federal Aviation Administration's Boise Flight Standards District Office examined the aircraft following the accident and reported finding no mechanical malfunction of the aircraft's left wheel brake assembly. (refer to attached statement NARRATIVE #33)