Throw back then throw forward, becoming combative (6)
I believe the answer is:
bolshy
'combative' is the definition.
'throw back then throw forward' is the wordplay.
'throw' becomes 'lob' (lobbing is a kind of throwing).
'back' says the letters should be written in reverse.
'then' is a charade indicator (letters next to each other).
'throw forward' becomes 'shy' (shy can mean to fling).
'lob' written backwards gives 'bol'.
'bol'+'shy'='BOLSHY'
'becoming' is the link.
(Other definitions for bolshy that I've seen before include "Awkward" , "stroppy" , "Deliberately combative" .)