When the ball crosses of the touch line for a kick-in, regardless of where the ball crossed the touch line, the referee whose touch line the ball crossed must move to the position of the kick-in to monitor the placement of the ball and encroachment.  See Diagrams 3, 4, and 5.  The other referee shall take a position as the lead or trail referee depending upon the proximity of the kick-in to the goal and the direction of the kick-in.