If only two-line judges are used, they stand at the corners of the court closest to the right hand of each referee, diagonally at 1 to 2 m from the corner. Each one of them controls both the end line and sideline on his/her side (Diagram 10).
Where possible, it is recommended to have four-line judges. They stand in the free zone at 1 to 3 m from each corner of the court, on the imaginary extension of the line that they control (Diagram 10).
29.2.1 The line judges perform their functions by using flags (40 X 40 cm) as shown in Diagram 12 to signal:
29.2.1.1 the ball “in” and “out” (Rules 8.3 & 8.4) whenever the ball lands near their line(s);
29.2.1.2 the touches of “out” balls by the team receiving the ball;
29.2.1.3 the ball touching the antenna, the served ball and the third hit of the team crossing the net outside the crossing space, etc.;
29.2.1.4 any player (except the server) stepping outside of his/her playing court at the moment of the service hit;
29.2.1.5 the foot faults of the server (Rule 12.4.3);
29.2.1.6 any contact with the top 80 cm of the antenna on their side of the court by any player during his/her action of playing the ball or interfering with the play; (VC Guideline 2.4)
29.2.1.7 ball crossing the net outside the crossing space into opponent's court or touching the antenna on his/her side of the court.
29.2.2 At the first referee’s request, a line judge must repeat his/her signal.