Brown shirt on suspect fit (7)
I believe the answer is:
tantrum
'fit' is the definition.
(I know that fit can be written as tantrum)
'brown shirt on suspect' is the wordplay.
'brown' becomes 'tan' (tan is a kind of brown).
'shirt' becomes 't' (as in a T-shirt).
'on' says to put letters next to each other.
'suspect' becomes 'rum' (I've seen this in other clues).
'tan'+'t'+'rum'='TANTRUM'
(Other definitions for tantrum that I've seen before include "Display of bad temper" , "Childish angry outburst" , "Childish outbreak of temper" , "Spoilt brat's fit" , "Hissy fit" .)