Possible Clues:

• Line that can't be crossed when firing arrows
• Starting point for darts players
• Line from 'Lepanto' (Chesterton)
• From which ricocheted the outer shot?
• Line in earth where river has disappeared
• Ring male that's caught in the firing line
• No cheat will overstep it?
• The line from which a darts player throws
• Line behind which a darts player stands
• Line to be observed when firing arrows