What variables can affect the attendence to a football game?

Weather is normally a large factor. The political situation might be a factor, for example if there had been a terrorist attack at a soccer match nearby recently, people might be afraid to go to other matches. Fans might boycott matches to prove a point to their team or to their local Football Federation. If a match is held during the working week in the middle of the day many people would not come. Those are just a few of the many possible variables.