Policemen are within their rights to stun (6)
I believe the answer is:
dismay
'rights to stun' is the definition.
I can't tell whether this definition defines the answer.
'policemen are within their' is the wordplay.
'policemen' becomes 'dis' (DI's, detective inspectors).
'are' becomes 'a' (short for 'are', historical unit of measurement).
'within' means one lot of letters goes inside another.
'their' becomes 'my' (I can't explain this - if you can you should believe this answer much more).
'a' placed inside 'my' is 'may'.
'dis'+'may'='DISMAY'
Can you help me to learn more?
(Other definitions for dismay that I've seen before include "Appal" , "Feeling of despair in the face of obstacles" , "Anxiety" , "Consternation, trepidation" , "Feeling of surprise and discouragement" .)