Football official leaving refused to be exploited (4)
I believe the answer is:
used
'be exploited' is the definition.
('used' can be a synonym of 'exploited')
'football official leaving refused' is the wordplay.
'football official' becomes 'ref' (ref is a kind of football official).
'leaving' indicates named letters should be taken away.
'refused' with 'ref' taken out is 'USED'.
'to' acts as a link.
(Other definitions for used that I've seen before include "Enjoyed" , "with some traffic" , "Of clothes or cars, second-hand" , "with a previous owner" , "Second-hand; exploited" .)