The pilot of the tailwheel-equipped airplane reported that during the landing roll, the tailwheel shimmied so he held full aft elevator input until the airplane slowed. He then "slightly" released the back pressure when the airplane suddenly swerved to the right. The pilot was unable to correct the turn and the airplane ground looped. The left main landing gear collapsed, and the left wing impacted the ground.
The airplane sustained substantial damage to the fuselage.
The pilot reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.