Poor waiter, beset by official over strong drink (9)
I believe the answer is:
firewater
'strong drink' is the definition.
(I know that firewater is a type of strong drink)
'poor waiter beset by official over' is the wordplay.
'poor' is an anagram indicator.
'beset by' is an insertion indicator ('beset' could historically mean 'cover').
'official' becomes 'ref' (match official in football, say).
'over' shows that the letters should be reversed in order.
'ref' in reverse letter order is 'fer'.
'waiter' is an anagram of 'irewat'.
'irewat' going within 'fer' is 'FIREWATER'.
(Other definitions for firewater that I've seen before include "whisky" , "stiff drink" , "Strong alcoholic spirits" , "Strong alcoholic drink" , "Strong alcohol" .)