While the singer was singing,he fell off the stage and hurt his arm.等于When the singer fell __ __the stage and hurt his arm,he was singing.

While the singer was singing,he fell off the stage and hurt his arm.
等于When the singer fell __ __the stage and hurt his arm,he was singing.

While the singer was singing,he fell off the stage and hurt his arm.
= When the singer fell （down from） the stage and hurt his arm,he was singing..
当歌手在演唱时,他从舞台上摔下来,弄伤了手臂.
fall off,从……跌落.fall down from,从……上摔下来.

fell off from the stage

fell down from