NHRA 101
A drag race is an acceleration contest from a standing start between two vehicles over a measured distance. A drag racing event is a series of such two-vehicle, tournament-style eliminations. The losing racer in each contest is eliminated, and the winning racers continue until one remains.
Each race is started by an electronic device commonly called a Christmas Tree. On each side of the Tree are six lights: a circle of small blue lights at the top — the top half for pre-staging and the bottom half for staging — three larger amber bulbs, a green bulb, and a red bulb.
Two light beams cross the starting-line area and connect to trackside photocells, which are wired to the Tree and electronic timers in the control tower. When the front tires of a vehicle break the first light beam, the pre-stage beam, the pre-stage lights on the Tree indicate that the racer is about 7 inches from the starting line.
When the racer rolls into the stage beam, the front tires are exactly on the starting line. The stage bulbs light, indicating that the vehicle is ready to race. When both vehicles are fully staged, the starter will activate the Tree, and each racer will focus on the three large amber lights on his or her side.
Depending on the type of racing, all three amber lights will flash simultaneously, followed four-tenths of a second later by the green light (a Pro Tree), or the three bulbs will flash consecutively five-tenths of a second apart, followed five-tenths later by the green light (a Sportsman, or full, Tree).
Elapsed time (e.t.) and speed are monitored for each run. Upon leaving the staging beams, each vehicle activates an e.t. clock, which stops when the vehicle reaches the finish line. The start-to-finish clocking is the e.t. Speed is measured in a 66-foot speed trap that ends at the finish line. Each lane is timed independently.
The first vehicle across the finish line wins, unless, in applicable categories, it runs quicker than its dial-under or index (see “Handicap and Index Racing”). A racer also may be disqualified for leaving the starting line too soon, leaving the lane boundary, failing to stage, or failing a post-run inspection.