Sports photography is generally pretty expensive due to the need of accurate focusing lens's and camera bodys but if your not out there required to nail the shot every time and doing it for fun/favour you can get away with lesser kit.
This is what works for me
Shoot from a low down position (sit on a short stool) £4 from go outdoors
makes the person look more imposing for a better photo.
The technical side of things a fast shutter speed is required to freeze the action and a wide apperture to seperate your subject from the background (make it all blurry) so as a guide set it to apperture priority set it to the widest (lowest number) and see what shutter speed you can achieve you should be wanting over 1/640 as a minimum 1/1000th is prefered. If you need to up your ISO to get the shutter speed then up your iso blurry photos are no good to anyone.
Focussing set it to continuos focus mode AI servo on the canon system and use the most accurate focus point usually your centre one and gives you a larger area to point your focus point at the persons body. follow the player so half press the shutter so it focuses and locks on and keep the focus point on the player then squeeze the shutter fully to take the photo as they are moving and keep tracking the player.
Get the full body, ball and they face in shot, cutting off feet, arms, hands whatever generally doesn't work. Back of heads again not good and the ball just tells you what they are doing not looking like running in a field wearing football kit. the other thing to shoot is the person, they are probably not interested in everything else arround them so a long telephoto lens is needed to get in close.
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