Haylee Slaughter sends along a color-codes toolbox of phrases and non-verbal actions she put together for refs to use in communicating with players during the match.

The USAR referees resources page also has a bunch of training videos like the one I posted yesterday on various topics.  At least some of them seem to also be available on Vimeo.  Let's see how many of them I can put on this post before Weebly complains.

Here are the 2018/19 USA GMGs.  You can also find them here and from the USA Rugby referee resources page.  USA Rugby puts this document out each year as a guide to how various aspects of the game are to be refereed.  This is the document that answers the question "when is the ball out?", among others.

USAR has promised an updated GMG for 2020, but I haven't seen it yet.

In May 2019, World Rugby published guidelines for dealing with high tackles and shoulder charges.  The framework document lives here or in the pdf attached.  WR says:

Under Law 9.11, the referee is always entitled to issue a red or yellow card for anything that they deem to be reckless or dangerous.

However, the following guideline is intended to improve consistency in application of sanctions by distinguishing between dangerous tackles that warrant a penalty, yellow card or red card. The framework also supports protection of the head of both players by consistently and frequently sanctioning the tackle behaviour that is known to be the highest risk.

Here's a post from the MidSouth Rugby Referee Society site on communication.  http://msrrs.org/2018/02/17/effective-referee-player-communication/