an auxiliary line of merchandise a line that marks the side boundary of a playing field
If you are on the sidelines in a situation, you do not influence events at all, either because you have chosen not to be involved, or because other people have not involved you. France no longer wants to be left on the sidelines when critical decisions are taken
If someone or something is sidelined, they are made to seem unimportant and not included in what people are doing. He was under pressure to resign and was about to be sidelined. if you are sidelined, you are unable to play in a sports game because you are injured, or unable to take part in an activity because you are not as good as someone else
{i} line of merchandise that is secondary to the principal line; secondary business or activity; line that marks the boundary on a playing field (Sports); area located immediately outside the boundary on a playing field (Sports)
the boundary line that runs the length of the field along each side; a ball carrier or ball that touches or crosses the sideline is out of bounds