What was the average amount of spectators when the away team scored 14.7 (91)?
CREATE TABLE "round_4" (
  "home_team" text,
  "home_team_score" text,
  "away_team" text,
  "away_team_score" text,
  "venue" text,
  "crowd" real,
  "date" text
);
SELECT AVG("crowd") FROM "round_4" WHERE "away_team_score"='14.7 (91)';