take a dive
1. In boxing, to pretend to be knocked out by one's opponent. (Generally done as a means of rigging the outcome of the match, so as to exploit betting odds and trends.) Heavily favored to dominate the match against the challenger, the defending champion has been suspected of taking a dive in the championship match last Saturday.
2. In soccer (football), to fall to the ground and make a very ostentatious display that one is in pain and anguish after making contact with an opposing player. (Done so as to draw a penalty kick for one's team.) It is so obvious that player from England took a dive!
3. In the stock market, to very suddenly become lower in value, as of the shares in a company or in the market as a whole. News of the automaker's deceptive practice of cheating on emissions tests has caused the company's shares to take a massive dive this afternoon. The market took a dive over the weekend after rumors of England's exit from the Eurozone.