For about three hours two mornings each week, the thwack of wood paddle meeting plastic ball echoes throughout Koko Head District Park’s gym, accompanied by the nearly constant sound of laughter.

This is a group of around 25 fun-lovers, nearly all over age 50, with some born right after the end of World War II. If they’re afflicted with grumpiness, they leave it at home. There’s sweat and friendly competition, but mostly it’s grins and giggles.

And, of course, guffaws all around when Linda Goeas makes an outrageously bold prediction:

“Some year, this will be in the Olympics.”

The “this” she speaks of is pickleball — a hugely popular emerging sport, especially among seniors.

The sport looks and plays like a combination of tennis, table tennis, badminton and volleyball.

The International Federation of Pickleball’s website lists just 12 member nations at this point, so it could be a while before it gets its shot at the Olympic Games. But with the momentum generated via the enthusiasm of Goeas and 1,200 other official Pickleball Ambassadors nationwide (including 21 in Hawaii), who knows?

According to a Sports & Fitness Industry Association report, the U.S. had 2.46 million pickleball players in 2015, up from around 100,000 just five years prior. It has been widely named in recent years as America’s fastest-growing sport.

The number of players in Hawaii has doubled to over 1,000 in the past year, Goeas estimates. The Honolulu Department of Parks and Recreation has recognized the growth by adding pickleball lines to courts designed for other sports, she said.

What’s not to love about a pingpong match where you get to stand on the table? Or tennis where you spend more time whacking the ball than icing your knees? Or badminton with a much lower net?

The court is 20-by-44-feet, around the size of a badminton court. The net is 36 inches at the ends and sags to 34 inches in the middle.

The mini-tennis court format makes for some interesting finesse play at the net, as well as a safer game (no volleying is allowed within 7 feet of the net). The worst injury anyone gets from getting whacked by the ball is a “pickleball tattoo,” says Tracey Bennett, 81, as she proudly displays the barely visible bruise on her forearm.

In Hawaii the game is often called pukaball as the ball has holes in it. A skilled pickleball player can make the ball dance — especially in an outdoors game when it’s windy, or sometimes by accident.

“It’s just fun, and we do crazy things,” said Bennett, who is also a pickleball referee.

One reason for the sport’s growth is the aging population.

Older athletes enjoy it because you can work up a good sweat with less impact on joints, especially when played on an indoor basketball court.

Most of the folks playing at Koko Head on a recent Tuesday morning were retirees, and at least part-time refugees from other sports.

Jerry Joslin, 72, picked up pickleball in 2016.

“I played sports all my life, and played a lot of tennis,” said the retired Kapaa High School teacher and basketball coach. “But I hurt my knee so my tennis game was going downhill fast. Now I play tennis twice a week, I do this twice a week and I lift weights twice a week. On Sundays, I do laundry.”

Others made complete transitions from racquetball, golf, soccer and surfing, and some, like Joslin, still play multiple sports.

“This is so much easier on the legs,” said Candy Yoshida, 65, who also plays tennis and has lost 35 pounds since taking up pickleball a few years ago. “Another good thing is that there are free clinics, and they really teach the game, they don’t just talk about it. All you have to do is Google ‘pickleball’ and you’ll find a meet-up.”

The youngest player on this day was Brian Barling, 49, a professional handyman who enjoys kayaking and water skiing. He was playing his old favorite sport, racquetball, at Fort DeRussy when he first saw some people playing what would become his new favorite, pickleball.

“Racquetball is dying out. There’s a lot of racquetball in this,” he said. “I get sweat all over the court, diving for the ball.”

Goeas still plays soccer, but said pickleball is now her No. 1 sport. “I’m so hooked on the sport. Since I’m a widow, it’s the love of my life,” she said.

On some weekends, she shares a pickleball court with 7- and 8-year-olds.

That’s fitting, since the sport was invented in the 1960s as a children’s game. It’s still for kids — of all ages.