Even though a soccer team normally consists of eleven players, the books focus on four girls and their development. The friends have to prevail in an environment in which they have to fight hard for being taken seriously. The stories are about respect, conquering a presumably male domain, about loyalty and rivalry. They also tell of everyday life issues such as friendships, first love, jealousy, stress at school and domestic conflicts. The protagonists age during the course of the four books and live through different phases of puberty.