What it means
に反して means “against” or “contrary to.” It shows that a result, action, or situation differs from an expectation, prediction, rule, principle, or other standard. It commonly follows a noun phrase, such as an expectation or rule. It can also follow a plain clause nominalized with の, especially when describing a result that differs from what people expected or believed. The expression is somewhat formal and is frequent in written, explanatory, and news-style language.
Usage note
When it follows a plain clause, the pattern is plain clause + のに反して. In this pattern, の nominalizes the preceding clause; it is not the concessive expression のに meaning “although.” The expression can describe either a result contrary to an expectation or an action contrary to a rule, so the preceding noun or clause determines the precise meaning.
How to use it
予想に反して、試合は早く終わりました。
Contrary to the prediction, the match ended early.
多くの人が予想していたのに反して、桜は三月に咲きました。
Contrary to what many people had expected, the cherry blossoms bloomed in March.
予想に反して、試合は早く終わった。
Contrary to the prediction, the match ended early.
多くの人が予想していたのに反して、桜は三月に咲いた。
Contrary to what many people had expected, the cherry blossoms bloomed in March.