Center line fault?
 

I'm at AAU Nationals for a couple weeks, so eclectic a barrage of situations and questions.

First one. Setter jumps toward the net and lands with one foot completely across the center line, about 4 inches from the blocker's foot. There was no contact and no interference. Does this constitute a safety risk and a whistle? Or is it literally "no harm, no foul"?

Yes, it should be whistled, and yes, people will gripe about it when you do.