The flight instructor and student pilot were practicing landings to a turf strip. On the first landing, the touchdown was normal until the student pilot applied full right rudder followed immediately with full left rudder. The flight instructor attempted to regain directional control of the airplane and attempted a go-around. The airplane entered grass to the left side of the strip and the airplanes momentum slowed. The instructor reduced the engine throttle to idle and applied the brakes. The airplane continued to roll and collided with a ground depression from a nearby motocross track. Substantial damage was sustained to the fuselage and firewall. There were no reported mechanical malfunctions or failures prior to the accident.