Here are
some action shots I did recently with a K100D, Pentax 80-320 and Tamron 18-250. I assigned AF to the OK button and set AF to continuos focusing. Got more keepers than I thought. I think it is a good idea to shoot a little wider and do exact framing later on with cropping. Otherwise, things you want to have in the frame may move out of it before you can take the shot.
Try to avoid subjects coming towards you or running away from you directly. In other words, in terms of giving the AF a chance, the sideline is a better place to be than the goal line, unless you prefocus or subjects don't move towards you / away from you.