To beat one's victim is a bit fishy (7)
I believe the answer is:
lamprey
'a bit fishy' is the definition.
I can't tell whether this definition defines the answer.
'to beat one's victim' is the wordplay.
I cannot really understand how this works, but
'beat' could be 'lam' (I've seen this before) and 'lam' is present in the answer.
'victim' could be 'prey' (prey is a kind of victim) and 'prey' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for lamprey that I've seen before include "Freshwater eel-like fish" , "Eel-like animal" , "Marine carnivore" , "Fish-like vertebrate" , "seafood" .)