To amuse oneself; to amuse or engross oneself in something. Commonly used in the pattern '〜に興じる' (intransitive).
祭りで太鼓の演奏に興じる若者たちの姿が印象的だった。
The sight of young people enjoying themselves playing the drums at the festival was impressive.
子供たちは公園で鬼ごっこに興じていた。
The children were having fun playing tag in the park.
彼は週末に趣味の読書に興じる時間を大切にしている。
He values the time on weekends he spends engrossed in his hobby reading.