What is every value for rushing yards per game if the season is 1984?
CREATE TABLE "season_by_season_statistics" (
  "season" text,
  "points_per_game" text,
  "total_yards_per_game" text,
  "rushing_yards_per_game" text,
  "passing_yards_per_game" text,
  "sacks" text,
  "interceptions" text
);
SELECT "rushing_yards_per_game" FROM "season_by_season_statistics" WHERE "season"='1984';