Shortage of boxes? Shame, but no pressure (8)
I believe the answer is:
sparsity
'shortage' is the definition.
(I know that shortage can be written as sparsity)
'boxes? shame but no pressure' is the wordplay.
'boxes?' becomes 'spars' (sparring is a kind of boxing).
'shame' becomes 'pity' (synonyms).
'but no' is a deletion indicator.
'pressure' becomes 'p' (abbreviation).
'pity' with 'p' taken out is 'ity'.
'spars'+'ity'='SPARSITY'
'of' acts as a link.
(Other definitions for sparsity that I've seen before include "Thinly scattered state" , "Thinness of occurrence" , "Shortness of supply" , "Low density" , "Thinly-scattered state" .)