...damaged Oscar has tough part in Cats (7)
I believe the answer is:
cougars
'cats' is the definition.
(cougar is a kind of cat)
'damaged oscar has tough part' is the wordplay.
'damaged' indicates an anagram.
'has' indicates putting letters inside.
'tough part' becomes 'ug' (I can't explain this - if you can you should give a lot more credence to this answer).
'oscar' with letters rearranged gives 'coars'.
'coars' placed around 'ug' is 'COUGARS'.
'in' is the link.
Can you help me to learn more?
(Another definition for cougars that I've seen is " Pumas".)