Gamble if coming back in suit (5)
I believe the answer is:
befit
'suit' is the definition.
(I know that suit can be written as befit)
'gamble if coming back in' is the wordplay.
'gamble' becomes 'bet' (betting is a kind of gambling).
'coming back' shows that the letters should be reversed in order.
'in' indicates putting letters inside.
'if' written backwards gives 'fi'.
'bet' placed around 'fi' is 'BEFIT'.
(Other definitions for befit that I've seen before include "Become, suit" , "Be appropriate for" , "Be right and suitable for" .)