Guy become a personal trainer for a girl next door (possibly thanks to working for her father). They repeatedly ran on trails trough the woods behind their houses in the nude, and once met her school tennis coach there. The girl either was in it, or joined the tennis team then. He become support staff on the team and drove them around as they traveled for school tennis meets. Through pre-negotiating it turned out quite a few of the opposed players just happened to also be nudists or willing to try it, and they played quite a few games in the nude, though most of those without spectators I think. (And no, there wasn't NiS or any such broad nudity legalization involved.)
I think I read this elsewhere and it had nonsensical beginning that possibly might been artifact of that sites age restrictions. I also think it included quite a lot of gratuitous "now let's fuck" sex with random partners, while the naked tennis was unfortunately under-described.
I also may missremember or conflate things...
Other suggestions that broadly match the title in the nutshell are welcome too.
