Many officials struggle with the rule concept that defenders may move to maintain their advantage obtained from their initial legal guarding position.
Obtain and maintain.
First defenders must obtain LGP. We know that LGP is initially facing the opponent with two feet on the court and in bounds.
Then remember. defenders by rule MAY MOVE to maintain that legal guarding position.
Defenders may move LATERALLY, they may move DIRECTLY BACKWARD, they may move OBLIQUELY ( at a diagonal) BACKWARD to maintain their LGP.
Defenders may not move FORWARD in any manner and initiate contact with ball handlers.
The video clip below shows a defender who has established LGP move laterally in a successful attempt to maintain his initial advantage. This is demonstrated by his taking the contact on his torso.
This is an impressive piece of officiating in my view. There is a rotation in progress and this official who was the old center, doesn’t bail out to the trail position, but stays engaged in the action, referees the defense and gets the call correct.