Unusual rubies found on ringleader, a tough guy (7)
I believe the answer is:
bruiser
'a tough guy' is the definition.
('bruiser' can be a synonym of 'tough guy')
'unusual rubies found on ringleader' is the wordplay.
'unusual' indicates anagramming the letters.
'found on' says to put letters next to each other.
'ringleader' becomes 'r' (first letter of ring).
'rubies' anagrammed gives 'bruise'.
'bruise'+'r'='BRUISER'
(Other definitions for bruiser that I've seen before include "Large tough man, inflicts flesh discolourations" , "Strong aggressive person" , "Fighter -- bully" , "tough guy" , "Fighter - rues rib (anag)" .)