[throw] {sb} a (curveball|curve)

to introduce a surprising or unexpected element or challenge into a situation

The idiom "throw someone a curveball" originates from baseball, where a curveball is a pitch that suddenly changes direction as it approaches the batter, making it challenging to predict and hit. This expression is often used when someone is faced with a situation that catches them off guard or requires them to adapt quickly.

The reporter threw the candidate a curve by asking about his past drug use.
During the presentation, the unexpected technical issue threw the speaker a curveball.
She thought the job interview would be straightforward, but they threw her a curveball with a tricky problem-solving task.
The sudden change in project requirements threw the team a curve ball, causing them to revise their plans.
In the game of chess, my opponent threw me a curve by making an unusual move I didn't anticipate.