Off-roading is the activity of driving or riding in a vehicle on unpaved surfaces such as sand, gravel, riverbeds, mud, snow, rocks, and other natural terrain. Types of off-roading range in intensity, from leisure drives with unmodified vehicles, to competitions with customised vehicles and professional drivers. Off-roaders have been met with criticism for the environmental damage caused by their vehicles. There have also been extensive debates over the role of government in regulating the sport, including a Supreme Court case brought against the Bureau of Land Management in the United States.