Irregular activity cut short by associate bringing back detectives (8)
I believe the answer is:
sporadic
'irregular' is the definition.
(similar in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for sporadic that I've seen before include "Having separate patches" , "infrequent" , "Occasional - intermittent" , "Happening irregularly" , "Occurring now and then - cop raids (anag)" .)