The Argus Leader newspaper reports that some spectators were placed in the infield after the stands filled up.
Stewart was leading the race with five laps to go when he spun to avoid a slower car. He finished 17th in the World of Outlaws event. It was the first time he had raced a sprint car in South Dakota.
Stewart started his career on dirt tracks in Indiana. He now makes select appearances at dirt tracks in addition to his NASCAR Sprint Cup schedule. He has raced at the track in West Fargo, N.D., several times in the past few years.