Small numbers going around wild - they never settle (6)
I believe the answer is:
nomads
'they never settle' is the definition.
(I've seen this in another clue)
'small numbers going around wild' is the wordplay.
'small numbers' becomes 'nos' ('no' is an abbreviation for number; 'small' asks for a short form).
'going around' is an insertion indicator.
'wild' becomes 'mad' (similar in meaning).
'nos' enclosing 'mad' is 'NOMADS'.
(Other definitions for nomads that I've seen before include "Travellers" , "Damson for wandering tribes" , "Vagrant peoples" , "[DRIFTERS]" , "Gypsies" .)