If you are on the sidelines or do something from the sidelines, you are not actively involved in something.

Women have been on the political sidelines for too long - we must now work towards getting into power. 女性在政治上旁观已久——我们必须努力争取权力。

She could only watch from the sidelines as her brother's health deteriorated. 她只能眼睁睁地看着弟弟的身体垮下去。