Sack servant laid up inside (7)
I believe the answer is:
pillage
'sack' is the definition.
(I know that sack can be written as pillage)
'servant laid up inside' is the wordplay.
'servant' becomes 'page' (I've seen this before).
'laid up' becomes 'ill' (similar in meaning).
'inside' indicates putting letters inside.
'page' going around 'ill' is 'PILLAGE'.
(Other definitions for pillage that I've seen before include "Sacking" , "Loot" , "Violent stealing" , "Rob with violence" , "Plunder, sack" .)