Football knowledge

Being a football fan all these years, I am ashamed to admit that I had no clue what the little semi-circle was for, the on attached to the penalty box (Yes, football as in soccer, you Americans will just have to adjust!). After some swift googling, I realized that I did know back in the day, but just forgot about it. For those of you who are still clueless and are too lazy to google, the semi-circle marks the area in which players have to be outside when a penalty kick is being taken. Simple and kind of self-explanatory, yet I was clueless! I guess I wasn't a hardcore football fan at all!