have a ball

Who's afraid of Virginia Woolf? 最後の舞台ACT THREE, THE EXORCISMに入っています。
MARTHA [sleepy child]: No more games ... please. It's games I don't want. No more games.
GEORGE: Aw, sure you do, Martha ... original game-girl and all, 'course you do.
MARTHA: Ugly games ... ugly, And now this new one?
GEORGE [stroking her hair]: You'll love it, baby.
MARTHA: No George.
GEORGE: You'll have a ball.
最後に出てきた "have a ball" は何でしょう？　こう言う簡単そうに思われる表現の意味が分からないのでネイティブ同士で話しているのが時々さっぱり分からない事があります。　これは慣用句なのでしょう。
?・Cambridge English Dictionary: to enjoy yourself very much: "So how was the party last night?" "Oh, it was brilliant, - we had a ball!"
・Vocabulary.com: enjoy oneself greatly: “We had a ball at the party and didn't come home until 2 AM”
・Wiktionary: (idiomatic) To enjoy thoroughly; to have lots of fun or excitement.: The kids had a ball playing in the fountain.
多くのスポーツでボールが使われるのでこの慣用句はそこから来ているのかなと思いましたが違いました。
This idiom uses the noun ball in the sense of "a gala dance."
とAmerican Heritage Dictionaryに書かれていました。