While wrecks are common in all types of motor sports, wrecking is the entire point of a demolition derby. In this sport, drivers try to take out everyone else's cars, and the last car running wins. How do you take out everyone else's cars? Ram them with your own. In a demolition derby, you have to figure out how to inflict maximum damage on your competitors while keeping your own car alive.
What makes demolition derbies challenging is the fact that they're run in muddy pits, so getting traction and maintaining control of the car is difficult. What makes them even tougher is that most drivers try to ram the rear of their car into the front of other cars so they can protect their vital components, like their engine, while taking out the key car parts of the rivals. That strategy works well, but it means driving backwards. Trying to get out of a crowded mall parking lot during the holidays can make you want to release your inner demolition derby driver, but it's better for your insurance rates if you save that kind of rage for a real derby.