In Turkey futbol is king. Futbol games are a must see when in Istanbul. You will find that the fans are hardcore. They cheer super loud and are really intense about their love for their teams. I have attended games where there were even small fires set (although no need to worry) because of the excitement. Popular teams but of course not limited to are Galatasary, Fenerbahce, and my husband's favorite Besiktas. Don't expect any snacks like they have in the states. No hotdogs. But you can get diner sandwiches and coke. Also, don't be surprised if the person next to you is working on a large bag of sunflower seeds and smoking a cigarette. It's all a part of the spirited local flavor.
The previous answer is about football, so i want to talk about other sport events. Everyone knows that football is most popular sport in Turkey, just as all around the world. But there are too many good options worth to watch. Like Basketball. In Turkey there are too many good and succesful basketball teams (men and women), which are competing in local league, THY Euroleague, Euro Cup... You can watch their maches in Abdi İpekçi Dome, Sinan Erdem Dome, Fenerbahçe Sports Arena...
In short term if you're planning to visit İstanbul, you better take this note :) 12 - 16 December / The 11th edition of the FINA World Swimming Championships (25m) will take place in İstanbul. You will get chance to watch star names of swimming world, like Ryan Lochte, Federica Pellegrini... (for details)
