Cleats or studs are protrusions on the sole of a shoe, or on an external attachment to a shoe, that provide additional transaction on a soft or slippery surface. They can be conical or blade-like in shape, and made of plastic, rubber or metal. The type worn depends on the environment of play, whether it be grass, ice, artificial turf, or other grounds. In association football, where the shoes themselves are known as football shoes, there are three different cleat types. There are soft ground cleats which are made for wet weather. The soft ground cleats are always replaceable, and are almost always metal, so when they wear down they are easy to replace. There are firm ground cleats which are made for firm natural surfaces. In the UK, 'cleats' are universally known as studs. The term "sliding tackle" is considered a dangerous tackle made with the feet raised and the potentially damaging metal studs hitting the legs or feet of the opponent.