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One cause of confusion and a regular source of let situations is when players have to rotate around each other moving in and out of the front court. There are two clear cut positional extremes that may help you better understand the situation and the usual gray area in between where your sixth sense and experience is required.
When the striker is nearer the centre of the court because the ball is away from the side wall it is easier for the incoming player to move inside and up to get the drop as the striker moves out and back An example of this may be when a drop is played from a boast.
When the striker position is near to the side wall the space for the incoming player is up and round as the striker moves back and out. An example of this a counter drop situation.
The gray area is the tricky bit to clarify. The striker should initially move out or back depending on which extreme they are nearest, although also bear in mind they will be influenced by their shot quality and what they need to cover next. The incoming player can sometimes take a lead from the striker's initial movement and move the opposite way. However if the incoming player has seen the shot early or is panicking because they know they are in a bit of trouble then they will move before the striker has committed. It comes down to a fifty-fifty whether to move clockwise or anti clockwise, although influenced by previous situations in the match!
As an incoming player the preferred direction of movement is influenced by what shot you want to play next. Movement inside will make the crosscourt shot easier, for example the cross lob, whilst movement outside will open up the straight line for the drive perhaps. You may not find your path open to you and so may have to move the other way and adapt!
These guidelines will help you but you just need to accept that the fifty-fifties will result in some 'Lets'. The main principle is for players to accept there could be occasional contact and interference but still make every reasonable effort to clear and to reach the ball.