Scattered boxes with energy (6)
I believe the answer is:
sparse
'scattered' is the definition.
(I've seen this before)
'boxes with energy' is the wordplay.
'boxes' becomes 'spars' (sparring is a kind of boxing).
'with' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'spars'+'e'='SPARSE'
(Other definitions for sparse that I've seen before include "Meagre, scanty" , "Far from lavish" , "Thinly populated" , "rarely occurring" , "One's not at all thick" .)