Addressing Kelly with firmness (5)
I believe the answer is:
toned
'addressing kelly with firmness' is the definition.
I can't judge whether this defines the answer.
'addressing kelly' is the wordplay.
'addressing' becomes 'to' (I can't justify this - if you can you should believe this answer much more).
'kelly' becomes 'ned' (outlaw Ned Kelly).
'to'+'ned'='TONED'
Can you help me to learn more?
(Other definitions for toned that I've seen before include "In good condition (of muscles or skin)" , "Muscular" , "Noted (anag.)" , "Well-muscled" , "went well" .)