Norm is out of line where this couple's concerned (4)
I believe the answer is:
pair
'this couple's concerned' is the definition.
'pair' can be an answer for 'couple's' (synonyms). I am unsure of the remainder of the definition.
'norm is out of line' is the wordplay.
'norm' becomes 'par' (I've seen this in another clue).
'out of' means to remove the last letter (I've seen 'out' mean this).
'line' indicates putting letters inside.
'is' with its final letter taken away is 'i'.
'par' placed around 'i' is 'PAIR'.
'where' acts as a link.
Can you help me to learn more?
(Other definitions for pair that I've seen before include "Set of two" , "2" , "Cereal used as food" , "flight of stairs" , "Two ducks in one game of cricket" .)