With the ball in rectangle 4, in the corner furthest away to his right (Diagram 36 and
Diagram 37), between the free-throw line extended and the endline, the trail official
does not have responsibility for the ball and the play around it.
It is his primary task to watch situations away from the ball.
His main responsibility is the low post area on the weak side (side away from the ball),
paying careful attention to possible illegal screening situations.
The most important principle is that the trail official must penetrate to the freethrow
line extended (approximately) when the ball penetrates towards the basket
or the endline on a pass, dribble or shot, in order to better find the spaces
between the players.
In Diagram 38 and Diagram 39, the ball is in the restricted area (rectangle 5). This is the
one occasion on which both officials will be looking at the play around the ball,
especially in shooting situations.
The trail official takes responsibility for the flight of the ball, watching to see whether or
not it enters the basket, as well as offensive and defensive goaltending and interference.
It is also his duty to be especially vigilant on rebound situations, paying
particular attention to the perimeter players who may be trying to obtain the ball from
an unfavourable position.
In Diagram 40, the ball is located in rectangle 6, in the two-point field goal area. The
trail official is primarily responsible for the ball. However, if the ball goes to the basket,
especially along the endline, the lead official will assume responsibility for the play
around the ball. He must pay particular attention to the high and low post areas.
In Diagram 41, the ball is still in rectangle 6 and in the three-point field goal area. The
trail official watches the ball and the play around it, especially when a shot for a field
goal is attempted.
The trail official is also responsible for giving the direction of play for the throw-in
following the ball going out-of-bounds nearest to the sideline on his left.
It is vitally important to have close cooperation between the two (2) officials at all
times. This is especially the case when the ball is in rectangle 6. It is strongly
recommended that whenever the ball passes into a new area, according to the
rectangles, and there is a change of responsibility for on-the-ball coverage, the trail
official should adjust to the position of his partner.