Knock over tin? Leave Charlie a brandy (6)
I believe the answer is:
cognac
'a brandy' is the definition.
(Cognac is an example)
'knock over tin? leave charlie' is the wordplay.
'knock over' says the letters should be written backwards.
'tin?' becomes 'can' ('can' can be a synonym of 'tin').
'leave' becomes 'go'.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'can'+'go'+'c'='cangoc'
'cangoc' reversed gives 'COGNAC'.
(Other definitions for cognac that I've seen before include "Type of brandy" , "High-quality brandy" , "(French district famed for) fine brandy" , "strong drink" , "French town - French brandy" .)