Rule Number 5?
RULE 5
Server and Receiver
The players shall stand on opposite sides of the net; the player who first delivers the ball shall be called the Server, and the other the Receiver.
Case 1. Does a player, attempting stroke, lose the point if he crosses an imaginary line in the extension of the net,
(a) before striking the ball,
(b) after striking the ball?
Decision. He does not lose the point in either case by crossing the imaginary line and provided he does not enter the lines bounding his opponents Court (Rule 20 (e)) In regard to hindrance, his opponent my ask for the decision of the Umpire under Rules 21 and 25.
Case 2. The Server claims that the Receiver must stand within the lines bounding his Court. Is this necessary?
Decision. No. The Receiver my stand wherever he pleases on his own side of the net.