Tug back on stomach (3)
I believe the answer is:
gut
'stomach' is the definition.
(I've seen this before)
'tug back' is the wordplay.
'back' is a reversal indicator.
'tug' in reverse letter order is 'GUT'.
'on' acts as a link.
(Other definitions for gut that I've seen before include "Stomach, belly" , "Thread made from animal intestines" , "spare tyre" , "Material for violins" , "Intestine, or the stomach" .)