What is the average goals against average for those playing more than 78 games?
CREATE TABLE "goaltending_leaders" (
  "player" text,
  "years" text,
  "games_played" real,
  "goals_allowed" real,
  "goals_against_average" real
);
SELECT AVG("goals_against_average") FROM "goaltending_leaders" WHERE "games_played">78;