A beastly study? (7)
I believe the answer is:
zoology
'a beastly study?' is the definition.
'zoology' can be an answer for 'study?' (zoology is a kind of study). I am not certain of the 'a beastly' bit.
'beastly study?' is the wordplay.
'beastly' becomes 'zo' (I can't explain this - if you can you should believe this answer much more).
'study?' becomes 'ology' (ology is a kind of study).
'zo'+'ology'='ZOOLOGY'
(Other definitions for zoology that I've seen before include "Science of animals" , "Science of animal life" , "The scientific study of animals" , "Animal study" .)