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.
The drill 
The name "20-yard shuttle" is derived from the total yards that athletes travel during the drill. They start in the middle of a 10 yard distance with one hand touching the ground. The athlete then pushes off their dominant leg in the opposite direction for 5 yards. After covering this distance, as quickly as possible they reverse and go 10 yards in the opposite direction. Finally, they reverse direction again, ending the drill at the starting point. The procedure is timed.