Are Water Sports People Moving the Ocean Backward?

Yes. Water sports people are moving the ocean backwards, just as runners and walkers are rotating the earth backward. It is just the plainest of Newtonian physics, that 'equal and opposite reaction' law. The ocean is big and you are little, so when you push on the water and move forward a lot, the ocean is moving back only a teeny, tiny, infinitesimally small bit. Nevertheless, a bit. But the ocean is also soft, no matter how well you paddle, so some of the energy seeps out here and there, and that has to go into the equation, too. As for the earth? Yeah, it is bigger than you are. So when you push off, you go forward more dramatically than the earth goes backward, but it does go backward and it can be interesting to think of it that way.