If soccer players want to run quickly, then they need to be producing a lot of force against the ground. There are two ways to do this; firstly, we can produce this force via our muscles when our foot is on the floor, or, secondly, we can have our foot moving at a very high speed once it hits the floor. For elite sprinters, it is, of course, a combination of the two. So, ideally, you want to have a large range of motion in which to accelerate the foot towards to ground (requiring good front side mechanics); you want to be able to accelerate the foot downwards (requiring good hip extensor strength); you want to contact the ground in the optimal position (requiring good sprint mechanics), you want to be able to absorb and reuse much of the force you apply (requiring good foot and ankle stiffness), and you want to be able to produce force quickly (requiring an optimal level of strength and power).
Team players gets a lot of acceleration, start&stop and change of direction stimuli in the team practice in general… small sided games in particular. The problem though that it develops a rather restricted movement patterns and poor sprinting mechanics. You often see 12-year-old soccer players moving better than 22-year-olds. Fore obvious reasons, I suggest some time is spent doing linear sprinting of various lengths and intensities at all ages.
Physical performance is a key part of the modern game of soccer. France had blazing speed and athleticism. Russia had crazy outputs. How important are certain physical qualities for success in soccer?