Pilot Report
The pilot stated that the landing was normal but, during the rollout, the airplane began to porpoise. He applied rudder, which caused the aircraft to exit the runway onto the grass, where it came to a complete stop.
ATC Observations
Air traffic control personnel who observed the airplane on approach reported that the airplane was slow and had a high sink rate. The airplane subsequently collided with the ground, bounced, landed hard again, and slid off the runway to the right.
Damage Inspection
Examination of the airplane by maintenance personnel revealed that the nose gear was bent aft and the engine mounts and firewall were buckled in several places.