expression, adverb
contrary to expectations; unexpectedly
Fixed phrase used adverbially to introduce a result that differs from what was anticipated.
予想に反して、試験は簡単だった。
Contrary to expectations, the exam was easy.
予想に反して、彼は賛成した。
Unexpectedly, he agreed.
Also means 'unexpectedly', but 予想に反して emphasizes a direct contrast with a prior expectation.
Compound of 予想 (expectation) + に (particle) + 反して (te-form of 反する, 'to go against').