Most coaches recognize that any player who can power clean a big weight is probably going to be a terror on the field. The fact is, the power clean to bodyweight ratio is better at predicting vertical jump and 40 yard dash performance than any other method outside of actually jumping or running the 40.
But football coaches don't need to read some study in a scientific journal to figure this out. They can see with their own eyes that when the kid who has a big power clean hits someone he knocks them on their ass.
The power clean is often referred to as the athlete's lift. Cleans build and display power. This is the kind of strength that applies to sports.
The movement starts at the floor with the bar motionless, then the bar is steadily accelerated upward until somewhere between the knee and the hip where an all-out explosion occurs. The slow acceleration from the floor, along with the explosion at the end, together have to impart enough speed and momentum to the bar to raise it to the rack position on the shoulders.
Great force must be applied to the bar while it's moving upward at a high rate of speed. The bar must be accelerated to a speed of about 2 meters per second.
The reps per set are usually between 3 and 5. If you want or need to do more volume it makes more sense to do more sets and keep the reps the same. I usually program sets of 3 because it's a more complex movement. Doing 3 to 5 sets of 3 reps early in the week and then 1 or 2 heavier sets of 3 reps later in the week works well for the power clean.
An athlete can usually perform 5 sets of 3 with around 85 to 90% and a single set of 3 with 92% of his or her one rep max.