Rugby people may be mostly moving single set of rugby posts? (7)
I believe the answer is:
english
'rugby people may be mostly moving' is the definition.
I can't judge whether this definition defines the answer.
'single set of rugby posts?' is the wordplay.
'set of' indicates anagramming the letters (I've seen 'set' mean this (instruction to set the letters)).
'rugby posts?' becomes 'H' (rugby goalposts resemble the letter H).
'single' is an anagram of 'englis'.
'englis'+'h'='ENGLISH'
Can you help me to learn more?
(Other definitions for english that I've seen before include "spin?" , "Language of the shingle?" , "The nationality in his glen" , "International language, by assumption" , "Race" .)