Tricked by small fish (4)
I believe the answer is:
shad
'fish' is the definition.
(I know that shad is a type of fish)
'tricked by small' is the wordplay.
'tricked' becomes 'had' (to have someone can mean to trick them).
'by' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'had' put after 's' is 'SHAD'.
(Other definitions for shad that I've seen before include "fish that's been caught" , "Herring-like fish" , "Fish; dash (anag.)" , "Fish related to the herring" .)