What is Tries Against, when Tries For is 21?
CREATE TABLE "pool_2" (
  "team" text,
  "tries_for" text,
  "tries_against" text,
  "try_diff" text,
  "points_for" text,
  "points_against" text,
  "points_diff" text
);
SELECT "tries_against" FROM "pool_2" WHERE "tries_for"='21';