What a game is played on decides how fast the ball runs, how players get injured, and how many events a venue can host. There are three families of outdoor surface, and a handful of stadiums that avoid choosing.
Natural, hybrid and artificial
Natural grass is the baseline. Hybrid grass, also called reinforced natural grass, combines natural lawn grass with synthetic fibres that make the pitch stronger and more resistant to damage. It is used for football, rugby, gridiron football and cricket stadiums and training pitches, and for events and concerts. The first generation appeared in the 1990s. Fibres can be injected into the sand with a tufting machine, mixed with cork and sand in a plant and laid, or supplied as a carpet through which the grass roots grow.
One well-known system, GrassMaster, was developed and patented in 1993 by Desso Sports of the Netherlands and is now sold by Tarkett Sports. A machine injects about 20 million polypropylene fibres into the soil, each 20 cm long and pushed 18 cm deep, so that 2 cm shows above the surface.
Artificial turf first went down in 1964 at a school recreation area in Providence, Rhode Island, and reached a wide audience in 1966, when AstroTurf was laid in Houston's Astrodome. Natural grass had been tried there in 1965, but it largely died under the roof, and the baseball team spent most of that season on painted dirt. AstroTurf has since become a generic word for synthetic turf of any make. Its environmental and health effects have been studied; the first major academic review was published in 2014.
Pitches that move
A closed or partly closed stadium is a poor place for grass, and a stadium that wants football, concerts and American football on the same day has a surface problem. A few venues solve it by moving the whole field.
- State Farm Stadium in Glendale, Arizona has a natural grass field on a tray that rolls in and out of the building. Business Week named it among the ten most impressive sports facilities in the world for the combination of its retractable roof and roll-in grass, similar to GelreDome and the Veltins-Arena.
- Allegiant Stadium in Las Vegas lays artificial turf directly on the concrete floor. When the grass tray is brought in, the turf is rolled up and kept beneath the stadium.
- Tottenham Hotspur Stadium in London has two surfaces: a GrassMaster hybrid pitch for football and synthetic turf underneath for NFL fixtures, concerts and other uses. The football pitch moves much as Arizona's does, but it is the first to divide into three sections as it goes, since two columns holding up the south stand block a single piece.