Two doctors needed for unruly crowds (4)
I believe the answer is:
mobs
'unruly crowds' is the definition.
(I've seen this in another clue)
'two doctors needed' is the wordplay.
'two doctors' can mean two substitutions for 'doctor'.
'doctor' becomes 'mo' (medical officer).
'doctor' becomes 'bs' (Bachelor of Surgery).
'needed' is a charade indicator (letters next to each other).
'mo'+'bs'='MOBS'
'for' is the link.
(Other definitions for mobs that I've seen before include "Unruly crowds" , "Disorderly crowds of people" , "riotous assemblies" .)