Fuzz stopping covert operative? That's smart (6)
I believe the answer is:
snappy
'smart' is the definition.
(snappy can mean smartly dressed)
'fuzz stopping covert operative?' is the wordplay.
'fuzz' becomes 'nap' (nap can refer to a piece of fuzzy fabric).
'stopping' indicates putting letters inside (stopping can mean blocking a gap).
'covert operative?' becomes 'spy' (I've seen this in another clue).
'nap' placed inside 'spy' is 'SNAPPY'.
'that's' acts as a link.
(Other definitions for snappy that I've seen before include "Ratty" , "Instantaneous" , "(Make it) quick" , "Quick and energetic" , "make it fast, so" .)