Maybe saw Rob coming back (4)
I believe the answer is:
tool
'maybe saw' is the definition.
(I've seen this before)
'rob coming back' is the wordplay.
'rob' becomes 'loot' (loot can mean to rob).
'coming back' says the letters should be written in reverse.
'loot' in reverse letter order is 'TOOL'.
(Other definitions for tool that I've seen before include "Cat's-paw; impress design on" , "Device, implement" , "Practical implement" , "Hand implement" , "one of 12 [SPADES] , for example" .)