Unexpected cops’ raid occurring irregularly (8)
I believe the answer is:
sporadic
'occurring irregularly' is the definition.
(I've seen this before)
'unexpected cops' raid' is the wordplay.
'unexpected' indicates anagramming the letters.
'cops'+'raid'='copsraid'
'copsraid' anagrammed gives 'SPORADIC'.
(Other definitions for sporadic that I've seen before include "infrequent" , "Fitful, intermittent" , "Having separate patches" , "Happening irregularly" , "Occurring at irregular intervals" .)