What's the umpire watching?

[TimTaylor]

The primary responsibility of the U during play is alignment of the recieve team, the net & centerline. They can also blow the whistle for something that is clearly out of the vision of the R.

Other than that, the U's responsibility is to support the R. Back row information is part of this, and is usually conveyed via discrete signals. Interestingly enough, a back row call (block or attack) is one of the few you can call retroactively at the end of the rally.

There's other information such as FR/BR position of setters that can be conveyed. Some R's want anything you can give them, others don't want much at all. You need to discuss this with your partner pre-match to work out the details.