Measure a piece of enclosed ground (4)
I believe the answer is:
yard
This might be a double definition.
'measure a piece' is the first definition.
'yard' can be an answer for 'measure' (I've seen this before). I am not certain of the 'a piece' bit.
'enclosed ground' is the second definition.
(enclosed outside area)
'of' is the link.
Can you help me to learn more?
(Other definitions for yard that I've seen before include "Sail support" , "Imperial unit of length" , "A little under a metre" , "3 feet" , "36 inches" .)