expression, adverb
obstinately; stubbornly; willfully
Describes doing something out of stubbornness or pride, often against better judgment. The phrase comes from 意地 (disposition, stubbornness) + になる (to become).
彼は意地になって、間違いを認めようとしなかった。
He stubbornly refused to admit his mistake.
意地になって反対するのはよくない。
It's not good to oppose something just out of stubbornness.
From 意地 (いじ, 'disposition, stubbornness') + に + なって (the te-form of なる, 'to become'). The phrase literally means 'becoming stubborn' and is used adverbially.