Volleyball - Special roles
Libero and back-row attacks, with the real trigger points.
The hard part of these calls is that the fault often is not the set or jump by itself. Officials ask who the player is, where the contact happened, and whether the attack ball was completed above the top of the net. That is why a play can look fine until the final hit.
Quick ruling: identify the player's role first. Then ask whether the action became a completed attack or block above the top of the net, and whether a libero's front-zone finger pass created a restricted attack.