This case study reviews the option shock, which occurred during the last ten minutes of trading on the expiry date of KOSPI200 options, Nov. 11th, 2010. KOSPI200 index plummeted by 2.79% on Nov. 11th 2010, which triggered the market collapse. By investigating participants’ behavior of the suspicious trading and their actual derivatives positions specifically, our study shows that the Nov. 11th Option Shock was the result of multiple violations of related regulations. Traders at an international securities company in Hong Kong made unfair profit with an intent to manipulate the market. Their colleagues in Korea also made money using the confidential trading information from the counterpart subsidiary in Hong Kong. The asset management firm placed option orders with trading amount well over the limit set by the regulatory code, and the local securities firm neglected to monitor the trading limit of the asset management. With these series of violations, billions of dollars of market capital evaporated, and investors lost millions of dollars. Similar incidences on the option expiration date have occurred all over the world. This study can provide the practical implications for policy makers and market participants. It also provides us with an excellent teaching opportunity in the areas of finance and business ethics.