Hang back to talk (3)
I believe the answer is:
gas
'talk' is the definition.
(gas can mean to chat)
'hang back' is the wordplay.
'hang' becomes 'sag' (I've seen this in another clue).
'back' says the letters should be written backwards.
'sag' backwards is 'GAS'.
'to' acts as a link.
(Other definitions for gas that I've seen before include "Empty talk (colloq.)" , "Domestic fuel" , "Eg, hydrogen" , "Something exciting" , "Talk idly; fuel" .)