Not fair, coach being out of sight of the house (8)
I believe the answer is:
offstage
'out of sight of the house' is the definition.
(I've seen this before)
'not fair coach' is the wordplay.
'not fair' becomes 'off' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'coach' becomes 'stage' (stagecoach).
'off'+'stage'='OFFSTAGE'
'being' is the link.
Can you help me to learn more?
(Other definitions for offstage that I've seen before include "out of sight of house" , "No longer acting" , "out of sight of the audience" , "Invisible to the audience" , "Not visible to the audience" .)