What really set it off was Kingsley's writing about something Newman had published and so far forgetting himself as to say (paraphrased) "like all Romans, Newman teaches that truth is no virtue."
THAT put the cat amongst the pigeons. Kingsley was an excellent writer and an effective polemicist, but he was entirely out of his league once Newman brought the big guns to bear on him.
Newman's reply to Kingsley ultimately evolved into his spiritual autobiography, Apologia pro vita sua (Apologia for ones life - you can't say apology because Newman used it in the Latin sense of defense or explanation, not the English sense of acknowledgement of fault.)
You can read the whole thing, including the original controversy, here.
thank you!