Paddy's drink's knocked over (5)
I believe the answer is:
strop
'paddy's' is the definition.
(I've seen this before)
'drink's knocked over' is the wordplay.
'drink's' becomes 'port's' (port is a kind of drink).
'knocked over' says the letters should be written backwards.
'ports' reversed gives 'STROP'.
(Other definitions for strop that I've seen before include "temper tantrum" , "Bad temper - sharpen (a razor)" , "Piece of leather on which razor is sharpened" , "Prime cutthroat" , "rage" .)