Scattered boxes on top of everything (6)
I believe the answer is:
sparse
'scattered' is the definition.
(I've seen this before)
'boxes on top of everything' is the wordplay.
'boxes' becomes 'spars' (sparring is a kind of boxing).
'on top of' indicates taking the first letters.
The first letter of 'everything' is 'e'.
'spars'+'e'='SPARSE'
(Other definitions for sparse that I've seen before include "Thinly dispersed" , "Thinly-spread" , "Thinly populated" , "Thinly dotted about" , "Far from lavish" .)