Was in charge of big bag for plunder (7)
I believe the answer is:
ransack
'for plunder' is the definition.
(synonyms)
'was in charge of big bag' is the wordplay.
'was in charge of' becomes 'ran' (I've seen this in another clue).
'big bag' becomes 'sack' (I've seen this in another clue).
'ran'+'sack'='RANSACK'
(Other definitions for ransack that I've seen before include "Loot or search thoroughly" , "Pillage, loot" , "Search thoroughly and roughly" , "Examine thoroughly" , "Plunder - rummage" .)