How does a kick-in work, and what is the four-second rule?

When the ball wholly crosses the touchline (or hits the ceiling), play restarts with a kick-in instead of a throw-in.

• The ball must be stationary on the touchline at the point where it left the pitch (or the nearest point to where it touched the ceiling).
• Only the kicker may be off the pitch.
• All opponents must be at least 5m from the point on the touchline where the kick-in is taken.
• The ball is in play when it is kicked and clearly moves.
• The ball must be put into play within four seconds of the team being ready or the referee signalling that the team is ready. If it is not, the kick-in is awarded to the opposing team.
• A goal cannot be scored directly from a kick-in. If the ball enters the opponents' goal, a goal clearance is awarded; if it enters the kicker's own goal, a corner kick is awarded.
• The kicker must not touch the ball again until another player has touched it, or an indirect free kick is awarded.
• An opponent who moves closer than 5m is cautioned for unsporting behaviour and, if the kick-in has been taken, an indirect free kick is awarded.