Слово за́ слово is a set phrase that means something like ‘a dialog turning into a fight’.
An example from a dictionary:
Базар is also a criminal-slang word for dialog or chatting.Слово за слово — схватились. Он мне два зуба вышиб, а я ему нос набок своротил.
Well, one word led to another, and we came to blows. He knocked two of my teeth out, and I bashed his nose sideways.
(sorry for my terrible English…)