Lawmen usually pursued by robbers (4)
I believe the answer is:
cops
'lawmen' is the definition.
(cop is a kind of lawman)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for cops that I've seen before include "Police (slang)" , "The police (sl.)" , "Familiar American policemen" , "Panda owners" .)