Rules of game are, we hear, maintained by writer (6)
I believe the answer is:
rubric
'rules of' is the definition.
The definition suggests a singular noun which matches the answer.
'game are we hear maintained by writer' is the wordplay.
'game' becomes 'RU' (rugby union).
'are we hear' becomes 'r' (I am not sure about this - if you are sure you should believe this answer much more).
'maintained by' means one lot of letters goes inside another (maintain can mean to keep hold of).
'writer' becomes 'bic' (kind of pen).
'r' placed inside 'bic' is 'bric'.
'ru'+'bric'='RUBRIC'
Can you help me to learn more?
(Other definitions for rubric that I've seen before include "Procedure rule (for exam, service)" , "Directions for conducting Christian services" , "Words put as a heading or direction as to how something must be done" , "Red title" , "Instructions at the head of a document" .)