The L-Drill, or 3-Cone Drill, is one of the major tests to evaluate football players every year at the NFL Combine, College Pro Days and other combines across the country. It's a great indicator of a player's quickness and ability to change directions. (Watch D1 head trainer Kurt Hester teach the essentials of the perfect 3-Cone Drill.)
Set up an L-shape with three cones, five yards apart from each other. The first cone is the start and finish line. The player sets up in a three-point stance with his hand behind the line. Timing begins on the player's movement. First, he sprints five yards and touches the line at the second cone with his right hand. Then he turns and sprints back to the first come, touching the line again. Next, he sprints again to cone two, makes a 90-degree turn to the right (dipping his right shoulder), and sprints five yards to cone three, where he makes a 180-degree turn (dipping his left shoulder) and sprints back to cone two. At cone two, he makes a 90-degree turn (dipping his left shoulder) and sprints through the finish line at cone one.
Here is a good video example: Jalen Manning (RB, '14, Smith County High School, Carthage, Tenn.)