Busy as one caught interrupting supply (7)
I believe the answer is:
officer
'busy' is the definition.
(busy can informally mean a police officer)
'one caught interrupting supply' is the wordplay.
'one' becomes 'i' (Roman numeral).
'caught' becomes 'c' (cricket abbreviation).
'interrupting' indicates putting letters inside.
'supply' becomes 'offer' (offer can mean to supply or provide).
'i'+'c'='ic'
'ic' put inside 'offer' is 'OFFICER'.
'as' is the link.
(Other definitions for officer that I've seen before include "Member of the armed forces in position of authority" , "Person with commission in armed services" , "Cop" , "Person holding authoritative position" , "Possibly a major" .)