I have always taken this literally:
- "when" meaning at the time it starts i.e at the time the throw or pass forward is made.
- a player is not throwing or passing a ball forward after it leaves his hands, or a hand, so the law is no longer relevant once it does.
- a throw or pass is not made forward if the ball is still in contact with a player's hands or a hand; so the law does not apply to the situation when there is still some hand contact, however tenuous. ***
- it follows that the law applies to the exact moment when it leaves the hands or a hand, as the referee judges it to the best of his ability.
The speed a player is running as he passes the ball, or what direction his hands are pointing as the ball leaves his hands, or what direction the ball takes after the exact moment it leaves his hands, are all irrelevant.
Always were, always are, always will be.
*** This is consistent with officials' rulings on tries. A try can be made in the act of (almost) losing the ball forward, or even backward, but it is grounded just before the moment it loses contact with the hands, or a hand.
In other words: there is no throw, or pass, until a hand loses contact with the ball.
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