#1 I dont like the crop, or lack of crop. The fence and the car are distracting. I like the lines he is making with his body, but to me, sports photography is about emotion and should always have faces with expressions in them (well, almost). The photo is also too centered in the frame
#2 Again, the photo is too centered in the frame. Would of loved a closer crop of the image where the kid with the red shirt is on the left hand side of the photo and the 3 on the wall fill out the right hand side. Seeing their faces much clearer would be great. Or a very close crop of all 3 of them with their hands on their crotch hehe
#3 Nice job capturing the kid in the red's expression, its what makes the picture.
You might crop it a bit closer to remove distractions on the sides. And as said, you definatly need a faster shutter to freeze the action.
#4 Same as #3, but a more interesting angle
Look for different angles to shoot from when at games. Shooting from behind the goal (if allowed) can give you better results. If you can't get there, look at being near the corners to try and capture the kids coming down the field. Straight on action shots and battles for the ball are what is interesting in the game. Those kind of things rarely happen with the kids running towards the sidelines. This would also help elimanate some of the fence/car/background distractions.
Also look for shots of the kids after a goal is scored, or the ones sitting on the bench with their heads in the hands, or a frantic coach.
As said, sports photos are all about a fast shutter speed. To do this, you need good light and good equipment. Try and get a shutter at 1/200 or faster at the very least. Its ok if the ball has movement in it, but not the person.
If you can't get a fast shutter speed, look for moments in the game where the action is a bit slower but there is still emotion, such as the goal keeper just getting the ball.