When in the 1st league position, how many people watch as they faced West Ham United?
CREATE TABLE "premier_league" (
  "date" text,
  "opponents" text,
  "result_f_a" text,
  "attendance" real,
  "league_position" text
);
SELECT MIN("attendance") FROM "premier_league" WHERE "league_position"='1st' AND "opponents"='west ham united';