Deliveries seized by mischievous beggar (10)
I believe the answer is:
impoverish
'beggar' is the definition.
(I've seen this before)
'deliveries seized by mischievous' is the wordplay.
'deliveries' becomes 'over' (I've seen this before).
'seized by' indicates putting letters inside.
'mischievous' becomes 'impish' (synonyms).
'over' placed into 'impish' is 'IMPOVERISH'.
(Other definitions for impoverish that I've seen before include "Spoil the quality of" , "beggar" , "Make poor" .)