sandbagging, tracks and series often invert some of the fastest qualifiers and start slower cars behind them. The number of cars to be inverted are typically not known to the drivers as they qualify, and often the fastest qualifier (who wins a cash bonus) will typically participate in a random drawing to determine the number of inverted cars after qualifying has concluded. Other tracks give bonus points to the fastest qualifier(s), which can drastically affect end of season awards. Still other tracks use "passing points" to reward the most cars passed in a heat race with a better chance to advance to the feature. Usually, the sandbagging is used only in shorter races where a pit stop is not used, such as heat races and in feature races of fewer than 100 laps in a United States Auto Club or World of Outlaws event. In most races of 125 laps or greater where a pit stop is required, inversion of fields is impossible because pit strategy negates the need for the inversion. To prevent sandbagging in World of Outlaws sprint car races, the winner and runner-up in each heat race, along with the two fastest qualifiers who have qualified for the feature but are not one of the top two drivers, participate in a short heat race-length race that determines the starting order for the first ten (or twelve if there are five heat races) starting positions in the feature. Demolition derby In demolition derby, a driver may hit other cars weakly or avoid contact with other cars to lessen the damage to their cars to ensure better odds of surviving to win the derby as the last car running. Events often require a car to hit another car within a certain time limit, usually every 120 seconds or less, or be disqualified. Rallying In some rallying series such as the World Rally Championship, the starting order in each race leg is determined by the overall standings of the previous leg. Because some track surfaces are faster once a few cars have passed, leading drivers may slow down in the final meters of the last stage of the first (and sometimes second) leg of the race and therefore let others clean the track the next leg. BMX racing USA: In BMX Racing, there are typically three levels of proficiency for amateur riders (ABA: Novice, Intermediate, Expert; NBL: Rookie, Novice, Expert).