In a sport known for its genteel traditions, tennis has one increasingly common ritual that stands apart for its ickiness — the passing of the sweat-soaked towel.

It happens dozens of times in a long match and is in full glory on the courts at Flushing Meadows: Players call for a towel to be brought to them in the middle of a game, and they quickly wipe the sweat from their faces, sometimes even their necks, arms and legs.

And then, in a fluid motion that's become part of the culture of the men's and women's tours, they casually toss the sweaty rag back to the barehanded ballkid, to be stowed neatly away for the next rubdown. Take my sweat, please.

Longtime observers of the sport say it's enough to put the eeeewwww in U.S. Open.

"If it's not your sweat, it's pretty gross," said U.S. Davis Cup captain Jim Courier, who has followed the trend both as one of the world's top players and now as a tennis broadcaster. "I don't think that I would want my child to be lifting a towel full of sweat. ... I don't think that should be part of the job description."

But it is.

"Some people might think it's disgusting but it's part of the job," said 16-year-old ballboy Marcus Smith of Queens. "We're here to help the players with whatever they need. You've got to do it."

So how did ballkids become de facto sweat valets for players? And why does it seem to be happening more than ever? Followers of the game say it's a trend set by big stars, and, ironically, rules designed to stop players from wasting time.

In years gone by, toweling off was largely an activity of the changeover. And if players really needed to mop sweat during a game, they took care of their own towel, keeping it at the back fence and retrieving it themselves.

Efforts to speed up the game — now a maximum 20 seconds between points at the Grand Slam events — ended up killing these do-it-yourself towel jaunts because they were too time-consuming within the confines of the rules.

Enter the scampering ballkids, whose frantic dashes to deliver the towel (often presented to the player like a toreador's cape) and retrieve the towel (often snagged out of the air from the player's no-look toss) have made the on-court rubdown time-friendly and all-too-easy.

While such players as Greg Rusedski and Andy Roddick were seen as pioneers in the practice of calling for the towel on nearly every point, some players say its popularity really took off with the rise of Rafael Nadal, whose frequent wipedowns have become legendary.

"Nadal brought in those methodical rituals to the game, whether it was an OCD or superstitious," said Bob Bryan, half of the world's No. 1 doubles team. "That goes to younger players and younger players — they emulate their idols and it just becomes part of the culture."

"Now everyone goes to the towel after every point," added brother Mike Bryan. "You don't need a wipe down after every point."

The practice has even spawned its own internationally recognized player-to-ballkid sign language for "bring me the towel" — a hand waving up and down in front of the face.

"It's gotten to be excessive," said Hall of Famer and Australian TV commentator Fred Stolle, who recalled how Nadal once gave towels to two ballkids on the same side of the court so they could deliver him his towel more quickly.

At this year's Australian Open, Nadal was sweating so much that ballkids were called out to clean up the sweat that sloshed on the court around where he was serving.

"It's not particularly attractive, no," said Courier, pointing out rubdown after rubdown on his bank of monitors in his television booth above Arthur Ashe Stadium. "I wish we could put the genie back in the bottle and say no towels until the changeover, but that's just not realistic."

Handling of sweat has become such a part the game that the U.S. Tennis Association has consulted a physician to come up with a "towel policy" for U.S. Open ballkids on how to deal with player bodily fluids.

"Sweat is absolutely fine" under the policy, explained the USTA's Tina Taps, who has supervised the U.S. Open's 250 ballboys and ballgirls since 1989. She said ballkids are encouraged to use hand sanitizer, available at all courts, and told to put bandages on any cuts they may have on their hands.

There is a limit, however.

"If a player should spit into towel, blow their nose into the towel, if there is any blood present, ballpersons are supposed to step back," said Taps, adding that just about everything has happened before. "The court attendant has gloves ... and takes the towel and puts it into a little hazmat bag."

Vanderbilt University infectious disease expert Dr. William Shaffner says that policy is in line with study after study that finds sweat — unlike saliva, mucus, vomit and blood — is not a vehicle for transmitting infections.

"The risk is close to zero. Basically, sweat is no sweat," Shaffner said. "That doesn't mean there's not a certain ick factor there."

Bob and Mike Bryan acknowledged they haven't given much thought to how ballkids feel about it all. That's because they know most ballkids are fans of the game first.

"When I was a ballkid at 10 years old, I didn't care what Andre Agassi did to that towel. I was going to hold it," Mike Bryan said.

Added Bob Bryan: "These kids are like, 'Give me your wristbands!' and they're drenched, and they put them on and they're like, 'Yeah!'"

So have any ballkids ever refused to handle a player's sweaty towel?

"Not a single one," Taps said. "It is almost like an honor to be able to work so closely with the player."

That was a sentiment reflected in interviews with several U.S. Open ballkids. Most wouldn't dream of letting a little sweat stop them from getting close to their idols.

Fifteen-year-old Danny Singer of Manhattan says the highlight of his ballkid career was when he got to work a match of one of his favorite players, Grigor Dimitrov.

"It's cool to hold a famous person's towel."