ST. LOUIS, Mo. — There’s a friendly but rigorous doubles match being played on the tennis courts at a local recreation complex.

The neon yellow ball sails back and forth over the net.

But it is not a tennis ball.

It is plastic and pocked with holes, like a shrunken Wiffle ball.

And the foursome is not playing with rackets. They are hitting the balls with paddles, ones that are a little bigger than those used for ping pong.

They are not playing tennis or ping pong. Or racquetball or badminton, for that matter.

They are playing pickleball.

More accurately, they are learning how to play pickleball, a game that takes elements of multiple racket sports and spins them into its own quirky conventions.

On this summer evening, the class instructor, Jay Hubert, has walked the group through some strategies, including the lob, a shot often used in tennis.

The hit should loop deep into the opponent’s court, “so you gain time to get your position back,” says Hubert, 29.

Because of its perforations, the pickleball has more float, slowing the rally and buying players time to get into position. A pickleball travels at about a third of the speed of a tennis ball.

The ball’s lightness means it’s harder to smash, so brute strength does not factor into pickleball as much as other court sports. And it introduces an element of randomness — sometimes the wind grabs the ball; sometimes it doesn’t bounce true.

Strathearn’s children had played the game in middle school P.E., so he was familiar with it when he saw the pickleball class offered through St. Louis Community College’s continuing education program.

On this night, Strathearn has challenged Hubert in a game of singles. Singles and doubles matches are played with the same boundaries, about the size of a badminton court.

With less ground to cover than in tennis — and fewer sharp stops and starts — the game is more welcoming to folks who might have knee or joint problems but still want a cardiovascular workout.

Pickleball is particularly popular in Florida and Arizona, attracting retirees who have hung up their other raquets.

Dan Marlowe and his wife, Christine, both 68, decided to try to get a grasp on the game before spending their first winter in Florida. They bought their own paddles and come early to practice before class.

They are partners in a doubles match, and they are losing — but not by much.

Hubert reminds them to switch positions after a point is scored, for the next serve.

“We like it where we are,” Dan Marlowe jokes.

Serving is another way pickleball equalizes the playing level. The ball is served underhand, and it must bounce in the opponents’ court before being returned. It has to bounce again before the serving team hits it back.

After that, the ball can be returned without a bounce — a volley — or played off the bounce, with a ground stroke.

“The serving rules are the hardest part of the game,” says Hubert, as he reviews them for the group.

Another pickleball idiosyncrasy is the nonvolley line that runs parallel to the net on each side of the court. The zone between the net and the nonvolley line is called the kitchen. Players in that zone have to let the ball bounce before returning it, preventing close-to-the-net slams.

The location of the hit is much more important than its power.

“The key, most of the time, is to hit the ball low over the net,” Hubert reminds the group as they grab drinks and stretch at the end of the hour-long session.

A man who is walking to his car after playing a round of tennis nearby stops near the slightly sweaty, slightly winded group.

“Pickleball, right?” he asks.

“Come play in the fall session,” Hubert tells him. “It’s a great workout.”