Former claimant seen in unattractive quarrel (9)
I believe the answer is:
plaintiff
'former claimant' is the definition.
'plaintiff' can be an answer for 'claimant' (I've seen this before). I am unsure of the 'former' bit.
'unattractive quarrel' is the wordplay.
'unattractive' becomes 'plain' (similar in meaning).
'quarrel' becomes 'tiff' (informal term for an argument).
'plain'+'tiff'='PLAINTIFF'
'seen in' is the link.
Can you help me to learn more?
(Other definitions for plaintiff that I've seen before include "one in suit" , "One bringing civil court case" , "Person who brings a legal action" , "Person bringing a legal action" , "Suitor" .)