Punch-up as tiffs develop? Not initially correct (9)

'punch-up' is the definition.
(both can mean a fight)

'tiffs develop? not initially correct' is the wordplay.
'develop?' is an anagram indicator (I've seen 'developing' mean this (letters developed into a new form)).
'not initially' means to remove the first letter.
'correct' becomes 'right' (right can mean correct).
'right' with its initial letter removed is 'ight'.
'tiffs' with letters rearranged gives 'fistf'.
'fistf'+'ight'='FISTFIGHT'

'as' acts as a link.