Volleyball block rules prevent you from blocking an opposing team's setter who's attempting to set a ball. You can block someone who's hitting a ball as long as you are separated by the net, but you can't block a player who is setting the ball to another player on their team.

Are you allowed to block a set in volleyball?

The receiving team is not allowed to block or spike the serve. (I.e., contact the ball above the top of the net.) A spiker must contact the ball on his/her own side of the net, but may in the course of the follow through reach over (but not touch) the net.

Do setters need to be good at blocking?

A setter should be able to identify the opponent's blockers and single out which one is the weakest. Since they can play in either the front or back row, setters need to be ready to block, dig and receive a serve on defense.