This study documents whether investor's performance and mood being affected football matches like other market-excluded factors or not. If this assumption consider as a truth then market prices could be affected substantially and market anomalies could be observed. It also means that an active trading strategy can be based on this anomaly and can be beaten market. This paper examines world cup football matches affect on the Istanbul Stock Exchange 100 (ISE100) Index returns and the weak form efficiency for ISE with a different approach. To test the market anomaly it will be used descriptive statistics and Mann-Whitney U Test.