Lawsuit involves rotter in dramatic fall (7)
I believe the answer is:
cascade
'dramatic fall' is the definition.
(I've seen this before)
'lawsuit involves rotter' is the wordplay.
'lawsuit' becomes 'case' (a legal case).
'involves' means one lot of letters goes inside another.
'rotter' becomes 'cad' (a cad is a dishonourable person).
'case' going around 'cad' is 'CASCADE'.
'in' acts as a link.
(Other definitions for cascade that I've seen before include "Torrent" , "Small waterfall or series of them" , "Rush" , "Waterfall or deluge" , "Series of small waterfalls" .)