curveball
n.a situation that is very unexpected and difficult to deal with. It comes from baseball, where a pitcher throws a ball that suddenly changes direction.
n.an unexpected and difficult-to-handle situation or event. Derived from the baseball pitch of the same name, which causes the ball to move in an unpredictable arc.
“The sudden change in the weather was a real curveball.”
“The manager threw a curveball at the team by announcing the project cancellation just before the deadline.”
“While the initial proposal seemed straightforward, the legal complications that arose during the audit proved to be a significant curveball that the board was unprepared to handle.”
From curve + ball.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.