Quiet force keeps returning fire for officer (7)
I believe the answer is:
Here is my best explanation:
'officer' is the definition.
'quiet force keeps returning fire' is the wordplay.
'quiet' becomes 'sh' (**).
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'keeps' is an insertion indicator.
'returning' shows that the letters should be reversed in order.
'fire' written backwards gives 'erif'.
'shf' going around 'erif' is 'SHERIFF'.
'for' is the link.
(Other definitions for sheriff that I've seen before include "Law enforcer", "Officer of the law", "Scottish judge", "Lawman of the wild west", "Crown's county officer", "Chief officer of the Crown in a county", "Chief Crown representative in a county", "An officer of the crown", "US law enforcement officer" and "Law enforcement officer".)