Angola! said:
So, a player can step on part of the line and that is OK? It is only when their entire foot crosses the line that it is a foul?
Also, do rotation errors always result in points?
And digger, are you a libero?
Ha! The screen name is kind of ironic, defense has always been my worst area. I know someone who has that real nickname, though, and I always thought it was cool.
On the centerline, the foot has to completely cross the line for it to be a fault. If you're on it (or hovering above it, say, if you're on you're tiptoes but the back of the foot is still over top of the line) you're ok. For serving, or 10-ball (back-row) attacks, if the foot touches the line before contact with the ball, that's illegal.
The rotation errors question is a good one - they always result in points (assuming this is rally scoring, not sideout scoring) when the ref blows the whistle for them. One example would be a wrong server (the team or a player get confused about where they are in the rotation and they don't follow the order - this isn't as rare as you'd think it is, I've seen really good, experienced teams do it). Another would be an overlap (players set up in the wrong position at the time the ball is served). Examples of this would be if the player who is supposed to be in the back left position starts the play in front of the person in the front left position. This most commonly happens with setters "cheating'' up to the front of the court and being in front of the front-row person she/he is supposed to be behind. It can also happen when teams have a sophisticated serve-receive that relies on two or three main passers and who thus have to each cover a big chunk of the court.
The reason I say it's a good question is that a lot of times overlaps happen, but aren't called (and therefore aren't a point). It's like the umpire in baseball who said "It ain't a strike until I say it's a strike''. Sometimes refs aren't good enough to recognize an overlap. Plus, they'll let "minor'' ones go on purpose, part of a recent trend in the game toward having the officials be more lenient to allow more actual play. (they're also allowing net violations that are not considered part of the play - say if the left side player somehow accidently touches the net for some strange reason when the set goes to the right side player. (it's extremely rare to have this actually happen).
Edited to put in a couple words where I didn't complete a thought! (in the centerline part)