NASCAR star Tony Stewart says he didn't see a young driver standing on a dirt track in upstate New York last year before he struck and killed him.

Stewart says in court papers Friday that he didn't realize Kevin Ward Jr. had been walking along the track after a crash at Canandaigua Motorsports Park on Aug. 9, 2014.

Ward's family has filed a lawsuit accusing Stewart of gross negligence, arguing he gunned his engine and put his car into a skid before hitting Ward.

Stewart's lawyer argues Ward caused his own death by getting out of his car and walking along the track.

Court papers say a toxicology report shows Ward smoked marijuana within five hours of the race.

An attorney for Ward's family did not immediately respond to an email seeking comment.