Fieldwork data from computer ignoring area around capital of Belgium (7)
I believe the answer is:
redoubt
'fieldwork' is the definition.
(I've seen this before)
'data from computer ignoring area around capital of belgium' is the wordplay.
'data from computer' becomes 'read out' (I've seen this before).
'ignoring' suggests deleting specific letters.
'area' becomes 'a' (maths abbreviation).
'around' is an insertion indicator.
'capital of belgium' becomes 'b' (I can't explain this - if you can you should believe this answer much more).
'readout' with 'a' removed is 'redout'.
'redout' placed around 'b' is 'REDOUBT'.
(Other definitions for redoubt that I've seen before include "temporary defence work" , "Defensive fieldwork" , "In final retreat" , "Obtrude in kind of military fieldwork" , "Tube rod (anag) - fortification" .)