a pitch that appears to be moving straight toward home plate but that is actually moving down and to the right or left by several inches
a pitch that often fools a batter
At the moment of releasing the ball, the pitcher twists the wrist, so it flies towards the pitcher from right to left for a right-handed batter, left to right for a left-handed batter, and dips just before reaching the batter.
A pitch thrown with a rotation that makes the ball curve.
Curveball was the designation for a claimed "Iraqi chemical engineer" who the United States claimed had served as an informant. Curveball would be the attributed source of pivotal information concerning weapons of mass destruction leading up to the 2003 Invasion of Iraq. The name Curveball is a reference to a curveball baseball pitch, which is US English slang for something that behaves indirectly, erratically, or surprisingly.