Dissenting group force lawsuit (7)
I believe the answer is:
faction
'dissenting group' is the definition.
(I've seen this before)
'force lawsuit' is the wordplay.
'force' becomes 'f' (abbreviation in physics e.g. f=ma).
'lawsuit' becomes 'action' (synonyms).
'f'+'action'='FACTION'
(Other definitions for faction that I've seen before include "A dissenting clique" , "Dissenting group - drama documentary" , "band" , "Wing" , "Clique that seeks power often through intrigue" .)