Not at all out of the ordinary and, when I was playing and what I hear now on the field, commonplace for officials and amongst team members.
Well, I actually I think it is a bit out of the ordinary in international rugby - hence why bikingbud noticed it back in Nov, and started the thread.
And I think we can be ptetty sure that (until now) Bud hasn't heard it since Nov (else he'd have reported back), and neither have I (as ditto)
But regardless - but what do actually think about the use of the phase "understand, boys?" from ref to players ... In that specific context.
Just trying to prise an actual opinion out of you!