The 40-yard dash is the marquee event at the combine. It's kind of like the 100-meters at the Olympics: It's all about speed, explosion and watching skilled athletes run great times. These athletes are timed at 10, 20 and 40-yard intervals. What the scouts are looking for is an explosion from a static start.
The vertical jump is all about lower-body explosion and power. The athlete stands flat-footed and they measure his reach. It is important to accurately measure the reach, because the differential between the reach and the flag the athlete touches is his vertical jump measurement.
The broad jump is like being in gym class back in junior high school. Basically, it is testing an athlete's lower-body explosion and lower-body strength. The athlete starts out with a stance balanced and then he explodes out as far as he can. It tests explosion and balance, because he has to land without moving.
The 3 cone drill tests an athlete's ability to change directions at a high speed. Three cones in an L-shape. He starts from the starting line, goes 5 yards to the first cone and back. Then, he turns, runs around the second cone, runs a weave around the third cone, which is the high point of the L, changes directions, comes back around that second cone and finishes.
The short shuttle is the first of the cone drills. It is known as the 5-10-5. What it tests is the athlete's lateral quickness and explosion in short areas. The athlete starts in the three-point stance, explodes out 5 yards to his right, touches the line, goes back 10 yards to his left, left hand touches the line, pivot, and he turns 5 more yards and finishes.