Grub found in lettuce at supermarket (4)
I believe the answer is:
eats
'grub' is the definition.
(I know that grub can be written as eats)
'in lettuce at supermarket' is the wordplay.
'in' indicates a hidden word.
'EATS' is hidden in the letters of 'lettuce at supermarket'.
'found' is the link.
(Other definitions for eats that I've seen before include "bits of food" , "Commonly, they eliminate" , "Is not any faster" , "Food (colloq.)" , "Grazes perhaps" .)