'Side line' definitions:

Definition of 'Side line'

From: GCIDE

Sideline \Sideline\, Side line \Side line\n. 1. (a) A line pertaining or attached to the side of a thing. (b) Specif., a line for hobbling an animal by connecting the fore and the hind feet of the same side. [Webster 1913 Suppl.]
2. A line of goods sold in addition to one's principal articles of trade; a course of business pursued aside from one's regular occupation. [Webster 1913 Suppl.]
3. A secondary road; esp., a byroad at right angles to a main road. [Canada] [Webster 1913 Suppl.]
4. (Sports) Either of two marked lines which delimit the side boundaries of a playing field, as in football or soccer. [PJC]
5. (Sports) [plural] The areas in a sports arena just beyond the sidelines[4], where coaches and alternative players sit or stand. [PJC]
on the sidelines not actively involved in an activity, such as a sporting event, but available for use when needed; in reserve; as, the coach kept him on the sidelines for a week. [PJC]