What match number has a ground of H and the opponent Chelsea under 18s?
CREATE TABLE "stats" (
  "match" real,
  "date" text,
  "competition_or_tour" text,
  "ground" text,
  "opponent" text,
  "score1" text
);
SELECT AVG("match") FROM "stats" WHERE "ground"='h' AND "opponent"='chelsea under 18s';