Rascal’s given one seafood (6)
I believe the answer is:
scampi
'seafood' is the definition.
(I've seen this before)
'rascal's given one' is the wordplay.
'rascal' becomes 'scamp' ('scamp' can be a synonym of 'rascal').
'given' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'scamp'+'i'='SCAMPI'
(Other definitions for scampi that I've seen before include "Crumbed prawns" , "Dish of cooked shrimps or prawns" , "Dish of fried shrimp or prawns" , "Prawn dish" , "Dish of crustaceans" .)