Basics of drag racing

Before each race (also known as a pass), each driver is allowed to perform a burnout, which heats the driving tires and lays rubber down at the beginning of the track, improving traction. Each driver then lines up (or stages) at the starting line. Races are started electronically by a system known as a Christmas tree. The Christmas tree consists of a column of lights for each driver/lane, one blue, then three amber, one green, and one red, connected to light beams on the track. The first, a split blue open circle, is split into two halves. When the first light beam is broken by the vehicle's front tire(s) indicate that the driver has pre-staged (approximately 7 inches (180 mm) from the starting line), lights the first half of the blue circle, and then staged (at the starting line), which lights up the second half of the blue circle, and also the corresponding bar in the middle of that circle.^{[1] [2]}
Below the blue "staged" light are three large amber lights, a green light, and a red light. When both drivers are staged, the tree is activated to start the race, which causes the three large amber lights to illuminate, followed by the green light. There are two standard light sequences: either the three amber lights flash simultaneously, followed 0.4 seconds later by the green light (a Pro tree), or the ambers light in sequence from top to bottom, 0.5 seconds apart, followed 0.5 seconds later by the green light (a Sportsman tree, or full tree). If the front tires leaves from a stage beam (stage and pre-stage lights both turned off) before the green light illuminates, the red light for that driver's lane illuminates instead, indicating disqualification (unless a more serious violation occurs). Once a driver commits a red-light foul (also known as redlighting), the other driver can also commit a foul start by leaving the line too early but still win, having left later. Should both drivers leave after the green light illuminates, the one leaving first is said to have a holeshot advantage.
The winner is the first vehicle to cross the finish line (and therefore the driver with the lowest total reaction time and elapsed time). The elapsed time is a measure of performance only; it does not necessarily determine the winner. Because elapsed time does not include reaction time and each lane is timed individually, a car with a slower elapsed time can actually win if that driver's holeshot advantage exceeds the elapsed time difference. This is known as a holeshot win.^[3]
Several measurements are taken for each race: reaction time, elapsed time, and speed. Reaction time is the period from the green light illuminating to the vehicle leaving the starting line. Elapsed time is the period from the vehicle leaving the starting line to crossing the finish line. Speed is measured through a speed trap covering the final 66 feet (20 m) to the finish line, indicating the approximate maximum speed of the vehicle during the run.
In the standard racing format, the losing car and driver are removed from the contest, while the winner goes on to race other winners, until only one is left.