So, if he were given only half a chance… (5)
I believe the answer is:
hence
'so' is the definition.
(thesaurus)
'only half a chance' is the wordplay.
'only' becomes 'he' (I am not sure about this - if you are sure you should believe this answer much more).
'half a' means to take half the letters.
'chance' cut in half is 'nce'.
'he'+'nce'='HENCE'
'if he were given' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for hence that I've seen before include "In the future; begone!" , "Therefore, consequently" , "It follows from that fact" , "For this reason; in the future" , "As a consequence" .)