throw someone a curve
throw (one) a curve (ball)
To do something unexpected or deceptive that surprises, confuses, thwarts, or outwits one. A curve ball is a pitch in baseball intended to be difficult to hit due to its curving path. Her confidence and fact-of-the-matter answers threw police a curve during their questioning. I had only been reading the textbook instead of going to classes, so a few of the questions on the final exam really threw me a curve ball.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
throw someone a curveor
throw someone a curve ballmainly AMERICAN
If someone throws you a curve or if they throw you a curve ball, they surprise you by doing something unexpected, sometimes causing you trouble. Just when they thought they might have the boss figured out, Knight would throw them a curve. Every so often Mother Nature throws us a curve ball. Note: You can refer to unexpected problems as curve balls. Once you get to know a person's habits and idiosyncrasies, there are fewer curve balls. Note: In baseball, a `curve ball' is a ball that curves through the air rather than travelling in a straight line.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012