Lawsuit in a court gets no-one's backing (6)
I believe the answer is:
action
'lawsuit' is the definition.
('action' can be a synonym of 'lawsuit')
'a court gets no-one's backing' is the wordplay.
'court' becomes 'ct'.
'gets' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'backing' says the letters should be written in reverse.
'no'+'i'='noi'
'noi' written backwards gives 'ion'.
'a'+'ct'+'ion'='ACTION'
'in' acts as a link.
(Other definitions for action that I've seen before include "war?" , "Operation; engagement" , "Battle (in the law courts?)" , "Lawsuit; thing done" , "Military engagement" .)