I feel bad backing youngster as intermediary (7)
I believe the answer is:
liaison
'intermediary' is the definition.
(I've seen this before)
'i feel bad backing youngster' is the wordplay.
'feel bad' becomes 'ail' (I've seen this in another clue).
'backing' says the letters should be written backwards.
'youngster' becomes 'son' (a child).
'i'+'ail'='iail'
'iail' reversed gives 'liai'.
'liai'+'son'='LIAISON'
'as' acts as a link.
(Other definitions for liaison that I've seen before include "Communication between groups or units" , "Cooperation between people or organisations" , "Intermediary" , "Go-between" , "Co-operation; love affair" .)