As Charles is no good at all, stop (4,2)
I believe the answer is:
rein in
'all stop' is the definition.
The definition and answer can be both to do with social activities as well as being verbs in their base form.
Perhaps you can see a link between them that I can't see?
'as charles is no good' is the wordplay.
I cannot really understand how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is found in the answer.
'no' could be 'n' (common abbreviation) and 'n' is located in the answer.
The remaining letters 'rei' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'at' is the link.
Can you help me to learn more?
(Other definitions for rein in that I've seen before include "Restrain (someone)" , "Control" , "Person of great power" .)