Paddy harbours upset (5)
I believe the answer is:
strop
'paddy' is the definition.
(I've seen this before)
'harbours upset' is the wordplay.
'harbours' becomes 'ports' (I've seen this before).
'upset' shows that the letters should be reversed in order.
'ports' backwards is 'STROP'.
(Other definitions for strop that I've seen before include "temper tantrum" , "Sharpen on piece of leather" , "Razor-sharpener" , "Display of temper" , "rage" .)