After an incredible run-up this year, the broader market trend was downward this week, to the tune of 1.6%, but some of the stocks out there were hit particularly hard. In this video, Motley Fool financial analysts Matt Koppenheffer and David Hanson take a look at what was behind three big dives this week: National Bank of Greece (NBG.DL), Newcastle Investment (DS), and American Capital Mortgage Investment (NASDAQ: MTGE).