Pinch small duck (5)
I believe the answer is:
'pinch' is the definition.
(I know that pinch is a kind of steal)
'small duck' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'duck' becomes 'teal' (teal is a type of duck).
(Other definitions for steal that I've seen before include "Rob" , "Make off with" , "Take illegally" , "Pilfer" , "Nick" .)