Falls for villain in trial (7)
I believe the answer is:
cascade
'falls' is the definition.
('cascade' can be a synonym of 'falls')
'villain in trial' is the wordplay.
'villain' becomes 'cad' (cad is a kind of villain).
'in' is an insertion indicator.
'trial' becomes 'case' (I've seen this in other clues).
'cad' going within 'case' is 'CASCADE'.
'for' acts as a link.
(Other definitions for cascade that I've seen before include "Shower" , "falls in the river" , "Series of small waterfalls" , "Waterfall or deluge" , "Dramatic fall" .)