His fault is going round the Nag’s Head (5)
I believe the answer is:
Here is my best explanation:
'his' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'fault is going round the nag's head' is the wordplay.
'fault' becomes 'vice' (I've seen this before).
'is going round' indicates putting letters inside.
'head' says to take the initial letters.
The initial letter of 'nags' is 'n'.
'vice' enclosing 'n' is 'VINCE'.