Defenders are required to obtain legal guarding position and maintain that position. It is important to know what a guard is able to do after legal guarding position is obtained.
Rule 4-23-2, “To obtain an initial legal guarding position, the guard must have both feet touching the playing court, and the front of the guard’s torso must be facing the opponent.”
In the following play, the primary defender gets beat on the spin move and the secondary defender moves in to help. It is questionable if the secondary defender is ‘two feet facing’ once the primary defender is beat. However, it is clear that the secondary defender did not move to ‘maintain’ a legal guarding position. Article 3c states, “the guard may move laterally or obliquely to maintain position, provided it is not toward the opponent when contact occurs.”
Here, when the contact occurs, the defender is turned sideways, moving into the dribbler. This should be ruled as a blocking foul because the defender, even if they obtained an initial position, did not maintain it by moving into the dribbler.