Unexpected Circumstances: Curveballs and Wrenches
A "curveball" is a type of throw in the sport of baseball where after being thrown, the baseball behaves unexpectedly. In phrases, the word “curveball” often can be a replacement for “disruptive event” or “surprising event.”
To be thrown a curveball, to throw a curveball
What is it?
To be thrown a curveball is to have an unanticipated event occur, with a neutral to negative connotation. The party that throws the curveball causes an unforeseen circumstance to happen, and the party to whom the curveball is thrown is disrupted or surprised.
Example: Lara is finishing a deal to sell her company's product to a buyer X. Hours before completing the deal, the buyer X tells Lara that a different seller is offering better terms. The buyer says that unless Lara can offer terms that are as good as the second seller's, they will not buy any products from Lara. Lara could say that the other buyer has thrown her a curveball.
To throw a wrench, throwing a wrench in the works
What is it?
“Throwing a wrench (into something)” has a similar meaning to “throwing a curveball.” To throw a wrench into something is to disrupt or dismantle plans. As with a curveball, the party that throws the wrench is the party that upsets or harms the receiving party. A difference from a curveball, is that where a recipient of a curveball may be a person, the recipient of a wrench would be that person's plans, project, or system.
Example: Lara is finishing a deal to sell her company's product to a buyer X. Hours before completing the deal, seller Y says that they are going to throw a wrench into Lara's deal, by offering better terms to buyer X than Lara is offering.