A back seat specialist (7)
I believe the answer is:
saddler
'a back' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'seat specialist' is the wordplay.
I cannot quite understand how this works, but
'seat' could be 'saddle' (saddle is a kind of seat) and 'saddle' is found within the answer.
A single letter 'r' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for saddler that I've seen before include "he'll offer you a seat" , "Maker of horse's equipment" , "One makes leather goods for horses" , "I'll make seat" , "Maker of seats for riders" .)