Betting on cat making big impression (6)
I believe the answer is:
splash
'big impression' is the definition.
(I've seen this in another clue)
'betting on cat' is the wordplay.
'betting' becomes 'sp'.
'on' is a charade indicator (letters next to each other).
'cat' becomes 'lash' (I've seen this before).
'sp'+'lash'='SPLASH'
'making' acts as a link.
(Other definitions for splash that I've seen before include "sensation" , "Big newspaper feature" , "Noise of a body falling into water" , "Big media display -- bellyflop effect" , "A Bigger --, Hockney painting" .)