Chief assistant is no southpaw (5-4,3)
I believe the answer is:
right-hand man
This clue could be a double definition.
'chief assistant' is the first definition.
(synonyms)
'no southpaw' is the second definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'is' acts as a link.
Can you help me to learn more?
(Other definitions for right-hand man that I've seen before include "Indispensable personal aide" , "Important assistant" , "Reliable assistant" , "One very much relied upon" , "Chief assistant; major domo" .)