From the above diagram, you can see there is a fine line for determining if a ball is actually ‘in’ or ‘out’. The rule of thumb is that if you can see the ball ‘out’ (a gap between the ball and the line) its ‘out’. If you do not see a gap and can’t determine if the ball is out, call it ‘in’.
1 Video: Pickleball Channel – Is the Ball In or Out?
f: Drop Shots