Listen in secretly, tumbling over spade (9)
I believe the answer is:
eavesdrop
'listen in secretly' is the definition.
(I've seen this before)
'tumbling over spade' is the wordplay.
'tumbling' is an anagram indicator.
'over'+'spade'='overspade'
'overspade' anagrammed gives 'EAVESDROP'.
(Other definitions for eavesdrop that I've seen before include "Listen secretly to private talk" , "Listen-in" , "spy" , "Snoop" , "Listen secretly to others' conversations" .)