Football is a popular sport played around the world. It is usually played on a rectangular field with two teams of 11 players each. The most common form of football is known as association football, or SOCCER, which is played with a round ball. Other forms of football include American football, which is played with an oval-shaped ball called a PIGSKIN, and rugby, which is played with an oval-shaped ball similar to a SOCCER ball. ARENA football is a variation of American football that is played indoors on a smaller field.