Few and far between, boxes on foremost of estates (6)
I believe the answer is:
sparse
'few and far between' is the definition.
(I've seen this before)
'boxes on foremost of estates' is the wordplay.
'boxes' becomes 'spars' (sparring is a kind of boxing).
'on' says to put letters next to each other.
'foremost of' suggests taking the first letters.
The first letter of 'estates' is 'e'.
'spars'+'e'='SPARSE'
(Other definitions for sparse that I've seen before include "Spares, being thin on the ground" , "Thin on the ground, scarce" , "In short supply" , "Meagre; scarce" , "Thinly populated" .)