Fall for rotter in action (7)
I believe the answer is:
cascade
'fall' is the definition.
(cascade can mean to fall or pour)
'rotter in action' is the wordplay.
'rotter' becomes 'cad' (I've seen this in another clue).
'in' indicates putting letters inside.
'action' becomes 'case' (synonyms).
'cad' placed into 'case' is 'CASCADE'.
'for' is the link.
(Other definitions for cascade that I've seen before include "Waterfall or deluge" , "Small waterfall or series of them" , "Rush" , "Tumble down (like water)" , "Sudden downpour" .)