Sudden police visit involving coppers (5)
I believe the answer is:
rapid
'sudden' is the definition.
(thesaurus)
'police visit involving coppers' is the wordplay.
'police visit' becomes 'raid' (I can't justify this - if you can you should give a lot more credence to this answer).
'involving' means one lot of letters goes inside another.
'coppers' becomes 'p'.
'raid' placed around 'p' is 'RAPID'.
Can you help me to learn more?
(Other definitions for rapid that I've seen before include "Flying" , "Swift, speedy" , "Speedy (5)" , "Zippy" , "Expeditious" .)