Social worker inhabiting empty trailer, I'm not sure fit (7)
I believe the answer is:
tantrum
'fit' is the definition.
(I know that fit can be written as tantrum)
'social worker inhabiting empty trailer i'm not sure' is the wordplay.
'social worker' becomes 'ant' (I've seen this in another clue).
'inhabiting' means one lot of letters goes inside another (I've seen this in other clues).
'empty' means to remove the middle letters.
'i'm not sure' becomes 'um' (expression of hesitation).
'trailer' with its middle removed is 'tr'.
'ant' put into 'tr' is 'tantr'.
'tantr'+'um'='TANTRUM'
(Other definitions for tantrum that I've seen before include "Wobbly" , "petulant outburst" , "Childish fit of anger" , "Hissy fit" , "Fit of ill-temper" .)