Rob Key's stuffing in last pie (5)
I believe the answer is:
steal
'rob' is the definition.
(I know that rob is a more specific form of the action steal)
'key's stuffing in last pie' is the wordplay.
'stuffing' means to look at the middle letters.
'in' indicates putting letters inside.
'pie' is an anagram indicator.
The centre of 'key' is 'e'.
'last' with letters rearranged gives 'stal'.
'e' inserted within 'stal' is 'STEAL'.
(Other definitions for steal that I've seen before include "a snip!" , "crib" , "Whip" , "Filch" , "Rob" .)