When did Riot Games release their 3D MOBA game?
CREATE TABLE "free_play" (
  "developer_s" text,
  "release_date" text,
  "required_os" text,
  "genre" text,
  "type" text
);
SELECT "release_date" FROM "free_play" WHERE "type"='3d' AND "genre"='moba' AND "developer_s"='riot games';