It's a man drunk showing vigour (7)
I believe the answer is:
stamina
'vigour' is the definition.
(I've seen this before)
'it's a man drunk' is the wordplay.
'it's a man' can be anagrammed to 'STAMINA'.
But, I'm not clear how the anagram is indicated.
'showing' is the link.
Can you help me to learn more?
(Other definitions for stamina that I've seen before include "Ability to maintain effort" , "resistance" , "perseverance" , "toughness in > male parts" , "Indefatigability" .)