The aim of these competitions is to be the last vehicle standing, after you have rammed every other car off the track. Thousands of such events are held around the US every year. The event starts with the driver's cars lined up in a circle on a dirt field, surrounded by a four-foot high wall of mud.
As the siren sounds, the cars begin crashing into each other. Helmets and seat belts must be worn, but other than that there does not seem to be other rules.