na-adjective, noun which may take the genitive case particle 'no'
half in fun; not entirely serious
Describes doing something with a playful, non-serious attitude, often implying that the action is not meant to be taken fully seriously.
彼は遊び半分で料理を始めたが、今ではプロ並みだ。
He started cooking half in fun, but now he's as good as a pro.
遊
You shouldn't buy stocks with a half-serious attitude.