Knocks back ginger biscuit (4)
I believe the answer is:
snap
'ginger biscuit' is the definition.
(I've seen this before)
'knocks back' is the wordplay.
'knocks' becomes 'pans' (I've seen this in another clue).
'back' shows that the letters should be reversed in order.
'pans' in reverse letter order is 'SNAP'.
(Other definitions for snap that I've seen before include "Break off - card-game" , "Spell of cold weather and card game" , "Break like informal photo" , "Sudden break" , "Informal photograph" .)