What was the average attendance on 18 October 2000?
CREATE TABLE "group_stage" (
  "date" text,
  "opponents" text,
  "h_a" text,
  "result_f_a" text,
  "attendance" real,
  "group_position" text
);
SELECT AVG("attendance") FROM "group_stage" WHERE "date"='18 october 2000';