The Trail has to get to the sideline and perhaps out of bounds to officiate the play. One good reason is if it's tableside, the coaches are going to get a better look at the play than the Trail if he/she stays at midcourt, even if he/she goes into the backcourt. And yes, the trail has to leave his/her sideline uncovered, but you're trading off missing a potential foul, to the risk that the trapped player is going to fling the ball 45 feet to the far sideline. Even if that happens, the trail has an unobscured look to see who it goes off of, if the Trail is at the sideline or OOB. And if the Lead is really awake, he/she will rotate over to balance the floor.
Get where you need to be to see the play.
(Disclaimer: Damien and I go to the same camps.
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