throw a wrench into

The phrase "throw a wrench into" is an idiomatic expression that means to introduce a problem, obstacle, or complication into a situation or plan, hindering its progress or causing difficulties. It suggests an action that disrupts or hampers the smooth functioning or execution of something. The origin of this expression is believed to be related to the idea of a wrench (or spanner) getting lodged or tangled in the moving parts of a machine, leading to a malfunction. Therefore, "throwing a wrench into" something metaphorically suggests disrupting or interfering with its intended flow or operation.