Slopestyle is a winter sport in which athletes ski or snowboard down a course including a variety of obstacles including rails, jumps and other terrain park features. Points are scored for amplitude, originality and quality of tricks. The discipline has its roots in action sports like skateboarding and BMX and has very successfully crossed over into the snow sports worlds of skiing and snowboarding. Skiers use Twin-tip skis for their symmetry since they often go large portions of the course backward (referred to as "switch") and for their balanced weight so don't destabilize spins. Slopestyle tricks fall mainly into four categories: spins, grinds, grabs and flips, and most tricks done in competition are a combination of these.