Can the receiver leave his service box after the server makes initiates the serve (i.e. makes contact with the shuttle)? Example: Is the receiver allowed to move forward out of his service box towards the net to return the serve or do his/her feet need to be within the service box when he first makes contact with the shuttle? I have a playing partner that leaps forward out of his service box like a wild gazelle to return my serves when I serve short. Would love to hear that he's cheating but from my interpretation of the rules it appears that he's allowed to leave the service box as soon as the server makes contact with the shuttle to initiate the serve.
You can return the service from any position on the court! But it's a fault if the receiver moves before you even hit the shuttle.
the receiver must be inside the box before the server strikes the shuttle. once after the server strikes the shuttle, it is anybody's game, the receiver can go anywhere he wants.
If the receiver moves before server strikes the shuttle . I think the OP is not sure if the receiver is allowed to move before he/she serves. The answer is correct - once after the server strikes the shuttle, the receiver can move. But if the receiver moves before server strikes the shuttle, then it is a fault. .
the last part of your question "he's allowed to leave the service box as soon as the server makes contact with the shuttle to initiate the serve" meaning you are not questioning whether a receiver is allow to or not prior to the serve...because he/she is not allowed. but as soon as you strike the shuttle, he's allow to go anywhere he wants. meaning...as soon as you strike the shuttle on a serve, your opponent is allow to spring forward like a wild gazelle to return your serves when you serve short.