Tragic news in the motocross community ... legendary pro racer Marty Smith and his wife Nancy were both killed in a freak dune buggy accident in California, TMZ Sports has confirmed.
He was 63.
Officials tell us Marty and Nancy were in a buggy that flipped at the Imperial Sand Dunes and rolled down a a hill. We're told Marty was not wearing a safety harness and Nancy was only wearing a lap belt.
We're told emergency responders raced to the scene -- but couldn't do much. Marty was pronounced dead at the scene.