Bit players unusually small (6)
I believe the answer is:
extras
'bit players' is the definition.
(I've seen this in another clue)
'unusually small' is the wordplay.
'unusually' becomes 'extra' (extra can mean to an unusual degree).
'small' becomes 's' (abbreviation - e.g. clothes size).
'extra'+'s'='EXTRAS'
(Other definitions for extras that I've seen before include "Bit actors in film" , "Crowd scene actors" , "Wides, byes, etc." , "Bit players in film" , "Ancillaries" .)