RIO DE JANEIRO (AP) — Ask a table tennis player to describe the most important part of the game and you usually get a single word answer: spin.

After that it gets more complicated.

There's topspin. Backspin. Sidespin. Side under spin. Side over spin. Heavy under/over/side spin. Light under/over/side spin. And, perhaps most devious of all, no spin.

In the course of a single Olympic match, it may all be there, and almost all of it will go unnoticed by spectators caught up in long, mesmerizing rallies filled with smashes, drop shots and miraculous defensive saves.

Spin is so crucial in table tennis that it's easy to determine its masters: Just look at the top 10 players in the world. But it's also a great leveler, allowing older and physically weaker players to hold their own and, sometimes, even beat the world's best.

And while the best players can determine what sort of spin is coming by the speed and angle of the bat's movement and the rotation and direction of the ball, the mechanics of spin are still something of a mystery. It is ubiquitous but imperfectly understood, sometimes even by the players who use it to perform feats that basement pingpong players can't even dream of.

Here then is a look at the Art of Spin.

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IT'S All IN THE WRIST (AND THE RUBBER)

Spin — sometimes mind-boggling, post-it-on-YouTube spin — is the backbone of Olympic-level table tennis.

But how do they do it?

It's all in the wrist — and the rubber.

No wrist movement means no spin. Rotate it like you're turning a key in a lock or slice it like you're executing a karate chop, and you'll make the ball spin, dance even, sometimes in unreturnable ways.

In his first- and second-round matches against players half his age, Spaniard Zhiwen "Juanito" He, a 54-year-old left-hander, employed spin constantly, his wrist slicing, swiveling and rotating, the ball seeming to veer in midair like a gunshot bird before glancing off the table and screeching off in another direction. He won the first and lost the second match, but his spin continually flummoxed his young opponents.

The type of rubber on the bat a player uses also matters. Thick rubber vs. thin. Hard vs. soft. Pimples out vs. pimples in. It all produces different kinds of spin.

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SPIN AS ZEN

Executing good spin requires that a tremendous number of different things all go right at the same time.

But to do it well, players must largely forget the details and just play.

"If you think, you have lost," said Thomas Weikert, president of the International Table Tennis Federation.

The trick to achieving a Zen-like level of spin is practice. Lots of practice, for hours a day, every day, for years on end.

"I know many athletes at the top of different sports, and ... they don't need too much practice since they are already good. But we always need practice," Dimitrij Ovtcharov, the German world No. 5 and the bronze medalist in London, said in an interview after a practice session at the Riocentro arena.

Ovtcharov notes two Chinese players practicing nearby, world No. 1 Ma Long and world No. 3 Xu Xin, who are rocketing the ball at each other in a rally that has lasted for what seems like half-an hour, their wrists flicking the ball so that it spins in a blur just over the net, each player progressively moving back from the table until they are 10 feet away, yet still putting the ball exactly where they want.

"They are practicing the whole day because of spin," Ovtcharov said. "Repetition after repetition will get you more feeling, and if you get more feeling you will react better under pressure."

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SPIN, DONE RIGHT, IS OFTEN UGLY — OR UNNOTICED

Another paradox about spin: Despite its importance, not many people watching the Olympics will realize it's happening at all.

The rapid rotation on the small ball is simply too hard to see.

Therefore, some spectators will be confused when an opponent botches a return of a masterful slow-topspin shot, for instance, wondering why that's so much harder to hit than a scorching smash.

Spin is also a great leveler.

When two players who know each other's game intimately play against each other, table tennis is often very fun to watch: long, exciting exchanges, with smash after smash.

"But if you don't know each other so well, the game doesn't look so nice sometimes because the players don't adapt to each other's spin," Ovtcharov said. "With no spin, the better one would have it a lot easier and there would be a lot less surprises."

The game is filled with specialists, like the Spaniard He, who deceive and frustrate their opponents with spin.

It's not always pretty, but it works.

Spin can often be seen in the games of "choppers," defensive specialists who use backspin to slowly chop an attacking opponent's ball back at them, over and over, negating attacks and waiting for a mistake.

It only works with spin.

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Online:

AP Summer Games website: http://summergames.ap.org/

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Foster Klug, AP's bureau chief in Seoul, South Korea, is covering table tennis and badminton in Rio. Follow him at www.twitter/apklug