The 20-yard shuttle, also simply called the short shuttle, is a test performed by American football athletes at the NFL combine. It is primarily run to evaluate the quickness and change-of-direction ability of players by scouts, particularly for the NFL Draft but also for collegiate recruiting. While not as highly regarded a test as the 40-yard dash, it is still an important barometer used by NFL personnel to compare players. Canadian football also uses the shuttle test.
The name "20-yard shuttle" is derived from the total yards that athletes travel during the drill. This drill is also known as the "short shuttle" or the "5-10-5" drill." The athlete starts at the center cone of 3 cones, each a distance of 5 yards apart. The athlete then pushes off their dominant leg in the opposite direction for 5 yards and touches the line. After covering this distance and touching the line as quickly as possible, the athlete must reverse and go 10 yards in the opposite direction and again touch the line. Finally, they reverse direction again, ending the drill at the starting point after traveling another 5 yards. The procedure is timed and the athlete starts the drill on reaction to the word "Go" as announced by the person starting the stopwatch. The NFL Scouting Combine allows each participant three opportunities to run the drill, and the best time of the three attempts is recorded as that players' time. 
This 20-yard shuttle drill is designed to measure short area quickness, lateral movement, flexibility and the speed at which a player can change directions. The drill also gives scouts an idea of how well a player can keep a low center of gravity as well as their ability to sink their hips.