I haven't shot soccer, but I do shoot lacrosse which is played on a similar sized field. If you're shooting from the sidelines, you may find that the 400 is too much lens, unless you just like to get head and shoulder shots. From the end line, 400 would be good for the far end of the field, but would be useless when the action comes down to your end. It helps to have two bodies, one with the 300 and the other with the 70-200 f2.8. I keep the 300 on a monopod, and just hold it in the crook of my left arm when the action gets close and I need to use the 70-200. Works well with the OpTech double strap and the Spider Holster kit.