Yes, it started in Southern California, and yes, it is often played by people wearing swimsuits, and yes, many of those people wearing swimsuits are beyond their swimsuit-wearing prime, but then, yes, it started in Southern California and those people are also swinging tennis rackets, which might ordinarily provide enough respectability to offset the swimsuit thing, except in this case they are not swinging tennis rackets on the tennis court but on the beach. Whatever. It’s Southern California, and the sport is called Beach Tennis, and, as this piece in the L.A. Times reports, it “provides an excellent workout for the glutes, quads and hamstrings and, to a
lesser extent, the arms. The sand not only forces the muscles to work
harder, it slows the game considerably, making it adaptable for seniors
and kids…”
The Rules:
The Times reports that Beach Tennis is played with standard tennis rackets and balls, and the goal is to
get the ball over the net. The scoring sequence  15, 30, 40  is the
same as in tennis, but there’s no deuce point, and players are allowed
only one serve. Beach tennis is played like badminton, in that the ball
is swatted back and forth, like a shuttlecock, and doesn’t hit the
ground. The net is four inches lower than a beach volleyball net, and
the court is 60-by-30 feet, similar to a beach volleyball court. The
winner is the first to win eight games, rather than the standard six in
tennis. Ideally,
the game is played with two people on each side, like doubles tennis.
The Danger: Singles games are strenuous, and games with more than two players per
side can be dangerous  teammates tend to get beaned by flailing
rackets.
More on Beach Tennis from USA Today.