On June 29, 2019, about 1850 mountain standard time, a Piper PA-28R-200, N786N, was substantially damaged when it was involved in an accident at Chandler Municipal Airport (CHD) Chandler, Arizona. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he was seated in the right seat and his son, who was not a pilot, was seated in the left seat at the time of the accident. The pilot reported that he often alternated seats on different flights for proficiency. They flew from Stellar Airpark (P19) to CHD to practice landings and takeoffs. The first touch-and-go landing on runway 22R was uneventful. The pilot reported that the second landing was normal, but, during the rollout, the airplane began to drift to the left and the left wing dropped. The pilot applied full right rudder to counteract the movement and the airplane yawed to the right. He applied brakes as the airplane moved to the right, but, seconds later, the left main landing gear collapsed, and the airplane came to a stop on the runway with the left wing and left stabilator contacting the runway. The nose landing gear and right main landing gear remained extended and locked, but the left main landing gear appeared to be mostly retracted into its wheel well. Examination of the recovered airframe revealed substantial damage to the left wing, stabilator, and empennage. The 1856 CHD special weather observation reported wind from 260° at 12 knots with gusts to 22 knots. Examination of the main landing gear system revealed that the landing gear lever was in the deployed position. The left landing gear was partially extended with the upper side brace link found with a smooth bend. The hydraulic actuator cylinder was extended and was still attached to the retraction bracket. The truss support bracket was displaced from its normal position on the wing spar, with its bolts and screws bent or broken. The left tire displayed radial scuff marks on the outboard sidewall.