Who was the partner that played a match on a grass court?
CREATE TABLE "doubles_6_3_titles_3_runners_up" (
  "outcome" text,
  "date" text,
  "surface" text,
  "partner" text,
  "opponents" text,
  "score" text
);
SELECT "partner" FROM "doubles_6_3_titles_3_runners_up" WHERE "surface"='grass';