One a policeman may have to nab, possibly? (5)
I believe the answer is:
baton
'one a policeman may' is the definition.
I can't judge whether this definition defines the answer.
'to nab possibly?' is the wordplay.
'possibly?' indicates an anagram (I've seen 'possibly' mean this).
'to'+'nab'='tonab'
'tonab' with letters rearranged gives 'BATON'.
'have' is the link.
Can you help me to learn more?
(Other definitions for baton that I've seen before include "Conductor's rod" , "Relay runner's stick" , "A stick for a conductor and policeman" , "It's used by a conductor and a policeman" , "Prohibition" .)