Scrap over a joint (6)
I believe the answer is:
shared
'joint' is the definition.
('shared' is associated in meaning with 'joint')
'scrap over a' is the wordplay.
I cannot quite see how this works, but
'over' could be 're' and 're' is found within the answer.
'a' is found in the answer.
This explanation may well be incorrect...
(Other definitions for shared that I've seen before include "Cut" , "Went halves" , "Communal" , "Possessed in common" , "Jointly possessed" .)