Hi, today during our practice someone and I were helping out people with their serves (we're no pros, but just teammate to teammate advice). One guy said that on your serve, you HAVE to slide your feet up to the line and then explode. I told him that its not his feet that are the problem (the guy being helped keeps his feet planted and doesn't move them up to the line) because pros like I think Aagassi, Sampras, and maybe federer don't drag, but he insisted that was the problem. I thought that it was more that he wasn't moving his momentum forward (and after he fixed this, he had much more power, so I think I'm right, but not positive), so I was wondering who was right? Was I right in saying it doesn't matter, or was he right that you have to move them forward?