Stealing from the fort (5)
I believe the answer is:
theft
'stealing' is the definition.
(I know that theft is a type of stealing)
'the fort' is the wordplay.
'fort' becomes 'ft' (abbreviation in place names).
'the'+'ft'='THEFT'
'from' is the link.
(Other definitions for theft that I've seen before include "Act of stealing" , "heavy crime" , "Taking of another's property" , "Burglary" , "Job" .)