You are doing well with fast shutter speeds to freeze the action, so that's really good. And as I said before, the are nice tight shots, which is much better than a photo of tiny players on a big field.
The focus does seam to be a bit of an issue on some shots...and as mentioned, it can be hard with gear that isn't ideal for shooting sports. One trick is to pre-focus, where you focus on an area where you expect the action to be...then start snapping when it gets there.