The position taken by the officials is constantly changing in accordance with the location of the players and the ball. If we divide the half-court up into six boxes the principle of sandwiching the play between the referees is easier to understand. 

The primary duties of the Lead Official are: 

1. Off the ball coverage when the ball is in boxes 1-3
2. Action in the 3-second area (Box 5). Players on offence can only stay in the ‘paint’ up to 3 seconds.
3. Not standing still when the ball is moving
4. Covering action on and around the ball, when it is in box 4 and 5

The primary duties of the Trail Official are: 

1. Field goal attempts (shots for basket)
2. On-the-ball coverage except when the ball is in box 4
3. To move in response to the movement of the ball