The best spot is on the sideline in a position to see between the defender and the ball-handler.
If the BH is too close to the sideline, then stay high behind the play and take only one step onto the court and open your shoulders to the play so you can see any approaching screens or secondary defenders while still officiating the primary matchup. Leaving one foot back near the sideline allows you to move out the way quickly should the play come back at you.
What not to do is take multiple steps onto the court and turn your back parallel to the division line so that you are facing directly towards the end line.
Optimal positioning for the Trail is sideline-oriented at the 28' line. When you establish that as your home base, subsequent position adjustments can be made more efficiently without radical movements.
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A-hole formerly known as BNR
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