Stick up and rob (3)
I believe the answer is:
mug
'rob' is the definition.
(slang)
'stick up' is the wordplay.
'stick' becomes 'gum' (I've seen this before).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'gum' reversed gives 'MUG'.
'and' is the link.
(Other definitions for mug that I've seen before include "Drinking vessel for one easily deceived" , "Vessel for a bit of a fool" , "Make a face" , "Large cup without a saucer" , "Face; cup; rob" .)