A playing field is a field used for playing sports or games. They are generally outdoors, but many large structures exist to enclose playing fields from bad weather. Generally, playing fields are wide expanses of grass, dirt or sand without many obstructions. More recently, some types of fields have begun using a synthetic grass-like material called AstroTurf, but its use is often controversial. Today a lot of fields have Next Turf, ProGreen or Field Turf. These Turfs are filled with rubber and/or sand.