Fiddler ____ (4)
I believe the answer is:
crab
'fiddler' is the definition.
(fiddler crab is a type of crab)
This is the entire clue.
(Other definitions for crab that I've seen before include "Clawed shellfish" , "Sideways scuttler" , "Sour character" , "Ten-legged shellfish" , "Pincered crustacean" .)