Fall of a rotter in a lawsuit (7)
I believe the answer is:
cascade
'fall' is the definition.
(cascade can mean to fall or pour)
'a rotter in a lawsuit' is the wordplay.
'a rotter' becomes 'cad' (a cad is a dishonourable person).
'in' is an insertion indicator.
'a lawsuit' becomes 'case' (a legal case).
'cad' going within 'case' is 'CASCADE'.
'of' acts as a link.
(Other definitions for cascade that I've seen before include "Outpouring" , "Rush" , "Tumble down (like water)" , "Torrent" , "Series of small waterfalls" .)