Scattered boxes primarily empty (6)
I believe the answer is:
sparse
'scattered' is the definition.
(thesaurus)
'boxes primarily empty' is the wordplay.
'boxes' becomes 'spars' (sparring is a kind of boxing).
'primarily' indicates taking the first letters.
The initial letter of 'empty' is 'e'.
'spars'+'e'='SPARSE'
(Other definitions for sparse that I've seen before include "Infrequent" , "Far from lavish" , "Thinly dispersed" , "One's not at all thick" , "Not much" .)