As part of a club competition, the pilot was required to carry out a practice forced landing on the strip. On the downwind leg the height of the aircraft was lower than desired and the pilot adjusted his tracking in order to converge with the strip. A continuous turn from downwind to final was attempted, during which the left wing suddenly dropped and the rate of descent increased. The pilot was able to regain partial control but the aircraft struck the ground heavily and ran off the side of the strip, colliding with rocks and scrub. After misjudging the height and distance to the selected touchdown point, the pilot elected to continue the approach. During the latter stages of the turn onto final, the aircraft probably encountered mechanical turbulence, which resulted in control difficulties and an increased rate of descent. It was likely that the pilot was influenced by the competition atmosphere existing at the time.