Mammal making racket (3)
I believe the answer is:
bat
This clue is a double definition.
'mammal' is the first definition.
(I know that bat is a type of eutherian)
'racket' is the second definition.
(I know that bat is a type of racket)
'making' acts as a link.
(Other definitions for bat that I've seen before include "Nocturnal animal - racket" , "Flutter (eyelids)" , "Nocturnal mouselike mammal" , "Club used in cricket" , "Cricketer; mammal" .)