Small team for prison guard (5)
I believe the answer is:
screw
'for prison guard' is the definition.
(synonyms)
'small team' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'team' becomes 'crew' (crew is a kind of team).
's'+'crew'='SCREW'
(Other definitions for screw that I've seen before include "Fastener with a tapered threaded shank" , "Threaded pin" , "Fixer; twist of paper" , "Tighten by turning" , "Prison officer (slang)" .)