Mean to add to the quarter yard (4)
I believe the answer is:
spar
'yard' is the definition.
(I've seen this before)
'mean to add to the quarter' is the wordplay.
'mean' becomes 'par' (average score on a golf course).
'to add to' means one lot of letters go next to another.
'the quarter' becomes 's'.
'par' after 's' is 'SPAR'.
(Other definitions for spar that I've seen before include "Shadow box" , "Box gently; main beam of aircraft wing" , "Length of wood" , "possibly rigged" , "Box in training - nautical pole" .)