Top policeman having change of heart (3)
I believe the answer is:
cap
'top' is the definition.
(both can mean to beat or outdo)
'policeman having change of heart' is the wordplay.
'policeman' becomes 'ca' (I can't justify this - if you can you should give a lot more credence to this answer).
'having' is a charade indicator (letters next to each other).
'change' becomes 'coppers' (as in copper coins).
'of heart' indicates the central letters (I've seen 'heart of' mean this).
The middle of 'coppers' is 'p'.
'ca'+'p'='CAP'
Can you help me to learn more?
(Other definitions for cap that I've seen before include "Outdo; brimless hat" , "'If the . . . fits, wear it' (3" , "subsidy regime" , "Soft hat; crown" , "Flat brimless hat" .)