Game with helpful person endlessly offering set of rules (6)
I believe the answer is:
rubric
'set of rules' is the definition.
(a rubric is a set of instructions)
'game with helpful person endlessly' is the wordplay.
'game' becomes 'RU' (rugby union).
'with' is a charade indicator (letters next to each other).
'helpful person' becomes 'brick' (brick can mean a reliable person).
'endlessly' means to remove the last letter.
'brick' with its last letter taken away is 'bric'.
'ru'+'bric'='RUBRIC'
'offering' is the link.
(Other definitions for rubric that I've seen before include "Red title" , "Words put as a heading or direction as to how something must be done" , "Document heading" , "Directions for the conduct of Christian services" , "Ruddy" .)