Mock small crop (5)
I believe the answer is:
scorn
'mock' is the definition.
(I've seen this in another clue)
'small crop' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'crop' becomes 'corn' (a farmer's crop of corn).
's'+'corn'='SCORN'
(Other definitions for scorn that I've seen before include "Look at with disdain" , "Spurn" , "Disgust" , "Open contempt, disdain" , "Mocking contempt" .)