Eat grass in a field (5)
I believe the answer is:
graze
'eat grass in a field' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for graze that I've seen before include "as some animals do" , "Eat grass; scrape skin" , "To eat constantly" , "Get one's oats" , "Bark (shin)" .)