An unintentional double hit is not a hindrance. It is not a hindrance if a player stops playing a point because he believed his opponent is being hindered. In this case the player loses the point. If a ball in play hits a bird, this is considered a hindrance and the point is replayed.
Decision: The server’s partner and the receiver’s partner may take any position on their own side of the net, inside or outside the court. However, if a player is creating a hindrance to the opponent (s), the hindrance rule should be used. USTA Friend at Court, ITF Rules of Tennis, Section 26. The way I would paraphrase this rule is as follows: A doubles team can stand any where in the court they choose and it is not a hindrance unless they actually create a hindrance.
For example, if you ask the server several times to stop discarding the second ball after serving, and the server continues to discard the second ball, the action is considered an intentional hindrance, and you can stop play immediately and claim the point when it happens.
Singles players should not talk during points. Talking between doubles partners when the ball is moving toward them is allowed. Doubles players should not talk when the ball is moving toward their opponent's court. When talking interferes with an opponent's ability to play a ball, it is a hindrance.
Also, it is not hindrance if a ball or any other object was lying on the player’s court when the point started. What about talking during play? For a singles match, talking is not allowed. And for doubles, talking is allowed between partners only when the ball is moving toward them. But if the ball is moving away from them, they should not talk.
Hindrance or Legit? If you just moved close to the box to intimidate the server, that would be fine; but by intentionally moving around, you create a Hindrance. Calling “Out” – Playing doubles, a high ball is coming towards your partner and you yell “Out!”; but he plays it anyway and hits it back to your un-ready opponents.
In tennis, since the players are on the opposite ends of the court, physical hindrance is rare. It is instructive to provide some examples. Up first is making a deliberate sound to hinder a player’s opponent. In case it isn’t obvious from the previous sentence, sound is essential for appreciating the hindrance in the following clip.
* Talking between doubles partners when the ball is moving toward them is allowed. * Doubles players should not talk when the ball is moving toward their opponent's court. * When talking interferes with an opponent's ability to play a ball, it is a hindrance.