Thwarts moles covering top of trap (6)
I believe the answer is:
spites
'thwarts' is the definition.
(I've seen this in another clue)
'moles covering top of trap' is the wordplay.
'moles' becomes 'spies' (I've seen this in another clue).
'covering' means one lot of letters goes inside another.
'top of' says to take the initial letters.
The initial letter of 'trap' is 't'.
'spies' enclosing 't' is 'SPITES'.
(Other definitions for spites that I've seen before include "Hurts out of malice" , "Deliberately hurts/annoys (someone)" .)