Paddy field filled by river (5)
I believe the answer is:
strop
'paddy' is the definition.
(I've seen this before)
'field filled by river' is the wordplay.
'field' becomes 'stop' (to field a ball is to stop its movement).
'filled by' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'stop' enclosing 'r' is 'STROP'.
(Other definitions for strop that I've seen before include "Strip of leather on which razor is sharpened" , "fit of anger" , "Sharpen an old blade" , "rage" , "Prime cutthroat" .)