Rascal gets one type of seafood (6)
I believe the answer is:
scampi
'type of seafood' is the definition.
(I've seen this before)
'rascal gets one' is the wordplay.
'rascal' becomes 'scamp' (synonyms).
'gets' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'scamp'+'i'='SCAMPI'
(Other definitions for scampi that I've seen before include "Breaded prawns" , "Large prawns cooked in batter" , "Dish of crustaceans" , "Fried seafood" , "Large sauteed prawns" .)